Composite gypsum board and methods related thereto

ABSTRACT

Disclosed is a composite gypsum board comprising a board core and a concentrated layer of substantial thickness (e.g., at least about 0.02 inches). The concentrated layer includes a higher weight percentage of an enhancing additive than the hoard core. The board core has a thickness greater than the thickness of the concentrated layer and forms the bulk of the board volume. The concentrated layer has a higher density (e.g., at least about 1.1 times greater) than the density of the board core. Also disclosed is a method of preparing a composite gypsum board.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims the benefit of U.S. Provisional PatentApplication Nos. 62/184,060, filed Jun. 24, 2015, and 62/290,361, filedFeb. 2, 2016, which are incorporated by reference.

BACKGROUND

Set gypsum (i.e., calcium sulfate dihydrate) is a well-known materialthat is used in many products, including panels and other products forbuilding construction and remodeling. One such panel (often referred toas gypsum board) is in the form of a set gypsum core sandwiched betweentwo cover sheets (e.g., paper-faced board) and is commonly used indrywall construction of interior walls and ceilings of buildings. One ormore dense layers, often referred to as “skim coats” may be included oneither side of the core, usually at the paper-core interface.

During manufacture of the board, stucco (i.e., calcined gypsum in theform of calcium sulfate hemihydrate and/or calcium sulfate anhydrite),water, and other ingredients as appropriate are mixed, typically in apin mixer as the term is used in the art. A slurry is formed anddischarged from the mixer onto a moving conveyor carrying a cover sheetwith one of the skim coats (if present) already applied (often upstreamof the mixer). The slurry is spread over the paper (with skim coatoptionally included on the paper). Another cover sheet, with or withoutskim coat, is applied onto the slurry to form the sandwich structure ofdesired thickness with the aid of e.g., a forming plate or the like. Themixture is east and allowed to harden to form set (i.e., rehydrated)gypsum by reaction of the calcined gypsum with water to form a matrix ofcrystalline hydrated gypsum (i.e., calcium sulfate dihydrate). It is thedesired hydration of the calcined gypsum that enables the formation ofthe interlocking matrix of set gypsum crystals, thereby impartingstrength to the gypsum structure in the product. Heat is required (e.g.,in a kiln) to drive off the remaining free (i.e., unreacted) water toyield a dry product.

The excess water that is driven off represents inefficiency in thesystem. Energy input is required to remove the water, and themanufacturing process is slowed to accommodate the drying step. However,reducing the amount of water in the system has proven to be verydifficult without compromising other critical aspects of gypsum board,e.g., commercial gypsum board product, including board weight andstrength.

Another challenge is reducing the weight of gypsum board whilemaintaining strength. One measure of the strength of board is “nail pullresistance,” sometimes simply referred to as “nail pull.” To reduce theweight of the board, foaming agent can be introduced into the slurry toform air voids in the final product. Replacing solid mass with air inthe gypsum board envelope reduces weight, but that loss of solid masscan also result in less strength. Compensating for loss in strength is asignificant obstacle in weight reduction efforts in the art.

It will be appreciated that this background description has been createdby the inventors to aid the reader, and is not to be taken as areference to prior art nor as an indication that any of the indicatedproblems were themselves appreciated in the art. While the describedprinciples can, in some regards and embodiments, alleviate the problemsinherent in other systems, it will be appreciated that the scope of theprotected innovation is defined by the attached claims, and not by theability of the claimed invention to solve any specific problem notedherein.

BRIEF SUMMARY

In one aspect, the disclosure provides a composite gypsum board. Thecomposite board comprises a board core comprising set gypsum formed fromat least water, stucco, and optionally, an enhancing additive. The boardcore defines first and second core faces in opposing relation and aconcentrated layer. The concentrated layer is disposed in bondingrelation to the first core face. The concentrated layer is formed fromthe enhancing additive, water, and, e.g., a cementitious material, suchas stucco, to form a hydrated cementitious material such as set gypsumin a continuous crystalline matrix. The enhancing additive is preferablymore concentrated (by weight percentage) in the concentrated layer thanin the board core. As used herein, any reference to the enhancingadditive being “more concentrated” (or variants of the term) in theslurry for forming the concentrated layer than in the slurry for formingboard core includes the situations where (a) both the concentrated layerand the board core are formed from enhancing additive, and (b) theconcentrated layer is firmed from the enhancing additive but the boardcore contains zero, or no, enhancing additive.

The concentrated layer has a density of at least about 1.1 times higherthan a density of the board core and has a thickness of from about 0.02inches (about 0.05 cm) to about 0.2 inches (about 0.5 cm) in someembodiments. The board core preferably has a thickness greater than thethickness of the concentrated layer. The enhancing additive includes astrength-imparting additive as described herein that helps producedesired strength properties as described herein.

Board formed from a concentrated layer slurry containing higher weightpercentage of the enhancing additive than contained in the board coreslurry allows for one or more efficiencies or process benefits. Forexample, the overall use of enhancing additive in the board can bereduced by focusing the enhancing additive in forming a smaller weightsection of smaller thickness (i.e., the concentrated layer) and usingless or no enhancing additive in forming a larger weight section oflarger thickness (i.e., the board core). Surprisingly and unexpectedly,the concentrated layer, formed from a higher weight percentage of theenhancing additive, is able to distribute the desired resultingproperties throughout the board core, such that the board exhibits thestrength properties. As a result, the board core can be made with lessoverall enhancing additive, and in some embodiments can be lighter andless dense than conventional board cores. In turn, overall board weightcan be reduced as the density in a large weight section of the board(i.e., the core) is reduced.

In the case of some enhancing additives, such as certain pregelatinizedstarches, they can require water in a slurry, i.e., they increase waterdemand. By reducing the amount of the enhancing additive in the slurryfor forming the board core, the water demand in the slurry for formingthe core can be reduced in sonic embodiments, Thus, for example, overallwater usage in preparing the board can be reduced, which further canimprove efficiencies as less water is used in the system such that lesswater is required to be driven off by heating in the kiln. As a result,manufacturing line speed can be improved and drying costs can bereduced.

The composite gypsum board can be within a range of desired densities.In some embodiments, the board can be made at ultra-light weights, suchas at a board density of about 33 pcf or less. It will be understoodthat board weight is a function of density and thickness. Thus, densitycan be used as a measure of board weight as will be understood in theart. Such ultra-light weights can be achieved without compromisingdesired strength properties. For example, in some embodiments, thecomposite gypsum board can exhibit a nail pull resistance of at leastabout 65 lbs of force (e.g., at least about 72 lbs of force, at leastabout 77 lbs of force, etc.) according to ASTM C473-10, Method B.

In another aspect, the disclosure provides a method of making compositegypsum board. The method comprises preparing a concentrated layer slurrycomprising water and the enhancing additive. The concentrated layerslurry can also include a base material to impart, e.g., a primarysource amass and density, such as a cementitious material, e.g., stuccothat can hydrate to form an interlocking matrix of set gypsum. Theconcentrated layer slurry is applied in a bonding relation to a firstcover sheet to form a concentrated layer having a first face and asecond face. The first face of the concentrated layer faces the firstcover sheet. The method also comprises mixing at least water, stucco,and optionally the enhancing additive, to form a board core slurry. Theboard core slurry is applied in a bonding relation to the concentratedlayer to form a board core. The board core has a first face and a secondface, wherein the first board core face faces the concentrated layersecond face. A second cover sheet is applied in bonding relation to thesecond board core face to form a board precursor. The board precursor isdried to form the board. When the board core slurry contains enhancingadditive, the concentrated layer slurry contains a higher weightpercentage of the enhancing slurry than the board core slurry. In someembodiments, the concentrated layer has a thickness of from about 0.02inches (about 0.05 cm) to about 0.2 inches (about 0.5 cm). When dried,the board core has a thickness greater than the thickness of theconcentrated layer.

In another aspect, the disclosure provides another method of makingcomposite gypsum board. The method comprises preparing a concentratedlayer slurry comprising water and the enhancing additive. Theconcentrated layer slurry can also include a base material to impart,e.g., a primary source of mass and density, such as a cementitiousmaterial, e.g., stucco that can hydrate to form an interlocking matrixof set gypsum. The concentrated layer slurry is applied in a bondingrelation to a first cover sheet to form a concentrated layer having afirst face and a second face. The first face of the concentrated layerfaces the first cover sheet. The method also comprises mixing at leastwater, stucco, and optionally the enhancing additive, to form a boardcore slurry. The board core slurry is applied in a bonding relation tothe concentrated layer to form a board core. The board core has a firstface and a second face, wherein the first board core face faces theconcentrated layer second face. A second cover sheet is applied inbonding relation to the second board core face to form a boardprecursor. The board precursor is dried to form the board, When theboard core slurry contains enhancing additive, the concentrated layerslurry contains a higher weight percentage of the enhancing slurry thanthe board core slurry. When dried, the board core has a thicknessgreater than the thickness of the concentrated layer.

Processes according to the disclosure can be used to produce compositeboard at any suitable density, In some embodiments, the board can bemade at ultra-light weights, such as at a board density of about 33 pcf(about 530 kg/m³) or less. Such ultra-light weights can be achievedwithout compromising desired strength properties. For example, in someembodiments, the composite gypsum board can exhibit a nail pullresistance of at least about 65 lbs of force (e.g., at least about 72lbs of force, at least about 77 lbs of force, etc.) according to ASTM0473-10, Method B, Other aspects and embodiments will be apparent fromthe MI description herein.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a schematic sectional view of a composite gypsum boardconstructed in accordance with principles of the present disclosure.

FIG. 2 illustrates schematic flow diagrams of three alternate processarrangements (labeled A, B, and C) that illustrate steps for preparingslurries for the board core and the concentrated layer in accordancewith principles of the present disclosure.

FIG. 3 is an illustration depicting a slurry head upstream of a rollerused in forming a concentrated layer on a manufacturing line for gypsumwallboard in a trial as discussed in Example 3 herein, wherein theslurry is absent glass fiber.

FIG. 4 is an illustration depicting a slurry head upstream of a rollerused in forming a concentrated layer on a manufacturing line for gypsumwallboard in a trial as discussed in Example 3 herein, wherein theslurry contains glass fiber.

FIG. 5 is an illustration depicting the slurry forming an edge aroundthe roller of the trial depicted in FIG. 3 as discussed in Example 3herein, wherein the slurry is absent glass fiber.

FIG. 6 is an illustration depicting the slurry forming an edge aroundthe roller of the trial depicted in FIG. 4 as discussed in Example 3herein, wherein the slurry contains glass fiber.

DETAILED DESCRIPTION

Embodiments of the disclosure provide a novel construction for acomposite board (e.g., gypsum board, such as wallboard) and a method ofmaking such board. As used herein, gypsum wallboard (often referred toas drywall), can encompass such board used not only for walls but alsofor ceilings and other locations as understood in the art. In oneaspect, the composite board contains multiple layers which containdifferent cementitious compositions, e.g., in the form of a continuouscrystalline matrix of set gypsum in the final product. One layer formsthe board core and another layer forms a concentrated layer ofsubstantial thickness (e.g., at least about 0.02 inches, or about 0.05cm). The board core is generally thicker than the concentrated layer inpreferred embodiments and makes up the bulk (e.g., over about 60%, suchas over about 70%, over about 75%, etc) of the volume of the board'senvelope. Typically, the board also includes top (face) and bottom(back) cover sheets.

The board core and the concentrated layer are both formed fromcementitious material and water. In accordance with preferredembodiments of the disclosure, the concentrated layer is formulated tohave a higher density than the board core has (e.g., at least about 1.1times higher). To formulate a lower density board core, foaming agentsas known in the art can be used in the board core, although othermaterials for reducing density can be included in the slurry for formingthe board core, as an alternative or additional ingredient, such aslightweight filler including, for example, lightweight aggregate orperlite, particularly if the additional expense can be accepted. Theconcentrated layer can include less or no foaming agent and/or less orno lightweight filler in order to achieve the desired higher density inthat layer.

While not wishing to be hound by any particular theory, it is believedthat the compositions of and inter-relationships between, the respectivelayers in the composite board impart surprising and unexpectedproperties in the product. In particular, it is believed that thetargeted use of enhancing additive in the concentrated layer can be usedto impart desired board properties, and enhance process efficiencies asdesired. In addition, in some embodiments, aspects such as (a) thethickness, density, and/or strength of the concentrated layer, and/or(b) the properties of the concentrated layer relative to the paper andthe board core, respectively, can be used to optimize board propertiesas desired. Based at least in part on these aspects, it is believed thatdesired properties from the concentrated layer can be distributed anddirected throughout the board, to thereby facilitate production of acomposite board while maintaining physical properties into the boardcore as desired.

In accordance with some embodiments, the dry concentrated layer has astiffness value that is closer to a stiffness value of the top coversheet to which it is generally adjacent. The concentrated layer has ahigher stiffness value than the board core in some embodiments. Thus,the concentrated layer can be disposed between a material withrelatively good stiffness and strength (i.e., the top cover sheet) and amaterial with less stiffness and strength (i.e., the board core) in someembodiments. It will be understood that stiffness value can be measuredaccording to Young's modulus as known in the art.

While not wishing to be bound by any particular theory, it is believedthat including a higher weight percentage of enhancing additive, whichimparts desired strength properties, in the concentrated layer resultsin effective desired strength properties. The concentrated layer isdisposed between a top cover sheet and a preferably lighter and weakerboard core. Surprisingly and unexpectedly, the concentrated layer servesto absorb energy from a load and more uniformly distribute the load intothe board core and throughout the board such that the load desirablywill more readily attenuate and dissipate. As such, the inventivecomposite gypsum board will demonstrate good strength properties andallow for lower weight board to be produced by targeting enhancedstrength in the concentrated layer where the property can be distributedinto the board core. For example, this advantage can be illustrated viagood results on a nail pull resistance and flexural strength tests insome embodiments, as is understood in the art in accordance with ASTM473-10, Method B.

Composition of Board Core and Concentrated Layer

In accordance with some embodiments of the disclosure, the compositegypsum board is tailored to include an enhancing additive in a higherconcentration than the enhancing additive is included (if at all) in theboard core. The resulting board can be formed to achieve a compositegypsum board with desired strength properties.

In accordance with some embodiments, it has been surprisingly andunexpectedly found that the higher concentration of the enhancingadditive in the concentrated layer relative to the board core results inefficient board performance with respect to desired strength properties,e.g., nail pull resistance, compressive strength, flexural strength,etc. As such, the present inventors have found that the usage of theenhancing additives can be optimized in accordance with preferredembodiments by tailoring the formulations of the compositions of therespective board core and concentrated layers to include enhancingadditives where their effect can provide more of an impact to achievedesired strength properties (i.e., in a higher weight percentage in theconcentrated layer than in the board core), and a lower overall waterdemand. This discovery imparts a considerable advantage including, butnot limited to, reducing overall enhancing additive usage and, hence,cost of the raw material, enhancing manufacturing efficiency, andenhancing product strength, e.g., allowing for lower weight product withsufficient strength properties.

In some embodiments, the slurry for forming the concentrated layercontains at least about 1.2 times the concentration of the enhancingadditive as compared with the slurry for forming board core, such as,for example, at least about 1.5 times, at least about 1.7 times, atleast about 2 times, at least about 2.5 times, at least about 3 times,at least about 3.5 times, at least about 4 times, at least about 4.5times, at least about 5 times, at least about 6 times, etc., whereineach of these ranges can have any suitable upper limit as appropriate,such as, for example, about 60, about 50, about 40, about 30, about 20,about 10, about 9, about 8, about 7, about 6.5, about 6, about 5.5,about 5, about 4.5, about 4, about 3.5, about 3, about 2.5, about 2,about 1.5, etc. It will be understood that “higher concentration,” asused herein, refers to relative amounts of an enhancing additive (byweight of the stucco), as opposed to gross amounts of ingredients. Sincethe board core provides a higher bulk volume and thickness contributionto the board, as compared with such contribution by the concentratedlayer, it is possible that any particular additive may be provided in ahigher total gross amount in the board core slurry, e.g., in pounds orkilograms, yet be provided in a lower weight concentration as comparedwith the slurry for the concentrated layer, i.e., in a lower relativeamount, e.g., in weight percentage (wt. %).

Surprisingly and unexpectedly, some embodiments of the disclosure areeffective in reducing the overall water usage in making the compositegypsum board. In this regard, by tailoring the respective compositionsof the concentrated layer and the board core, the total amount of waterused to make the board can be reduced such that water usage is optimizedsince the water is present in a higher concentration where it is neededmore (e.g., in the concentrated layer) and reduced where it is neededless (e.g., in the board core).

It will be understood that, since set gypsum is formed from a stuccoslurry (sometimes called a gypsum slurry) containing water and stucco, awater-to-stucco ratio (“WSR”) can be observed, In some embodiments, theboard core, which can form the bulk of the board volume, can be formedfrom a lower WSR as compared with the WSR used to form the concentratedlayer. Thus, the overall water usage and WSR in the composite gypsumboard as a whole can advantageously be brought down in some embodimentssince the contribution to the overall board volume by the concentratedlayer is less than the contribution to the overall board volume by theboard core.

The board core and concentrated layer can be formed from any suitableWSR. In some embodiments, the concentrated layer is formed from slurryhaving a WSR that is higher than the WSR of the slurry used to form theboard core, For example, in some embodiments, the concentrated layer isformed from a slurry having a WSR that is at least about 1.2 timeshigher than the WSR of the slurry used to form the board core (e.g., atleast about 1.5 times higher, at least about 1.7 times higher, at leastabout 2 times higher, at least about 2.2 times higher, at least about2.5 times higher, at least about 2.7 times higher, at least about 3times higher, at least about 3.2 times higher, at least about 3.5 timeshigher, at least about 3.7 times higher, at least about 4 times higheretc,, wherein each of these ranges can have any suitable upper limit asappropriate, such as, for example, about 7, about 6.5, about 6, about5.5, about 5, about 4,.5, about 4, about 3.5, about 3, about 2.5, about2, about 1.5, etc.)

In some embodiments, the board core is formed from stucco slurry havinga water-stucco ratio from about 0.3 to about 1.3, e.g., from about 0.3to about 1.2, from about 0.3 to about 1.2, from about 0.3 to about 1.2,from about 0.3 to about 1.2, from about 0.3 to about 1.1, from about 0.3to about 1, from about 0.3 to about 0.9, from about 0.4 to about 1.3,from about 0.4 to about 1.2, from about 0.4 to about 1.1, from about 0.4to about 1, from about 0.4 to about 0.9, from about 0.5 to about 1.3,from about 0.5 to about 1.2, from about 0.5 to about 1.1, from about 0.5to about 1, from about 0.5 to about 0.9, from about 0.6 to about 1.3,from about 0.6 to about 1.2, from about 0.6 to about 1.1, from about 0.6to about 1, from about 0.6 to about 0.9, from about 0.6 to about 0.8, orfrom about 0.6 to about 0.7.

In some embodiments, lower water-stucco ratios are preferred, e.g., fromabout 0.3 to about 0.8, such as, for example, from about 0.3 to about0.7, from about 0.3 to about 0.6, from about 0.3 to about 0.5, fromabout 0.3 to about 0.4, from about 0.4 to about 0.8, from about 0.4 toabout 0.7, from about 0.4 to about 0.6, from about 0.4 to about 0.5,from about 0.5 to about 0.8, from about 0.5 to about 0.7, from about 0.5to about 0.6, from about 0.6 to about 0.8, from about 0.6 to about 0.7,etc.

In some embodiments, the concentrated layer is formed from a slurryhaving a water-stucco ratio from about 0.7 to about 2, such as, forexample, from about 0.7 to about 1.7, from about 0.7 to about 1.4, fromabout 0.7 to about 1.2, from about 0.7 to about 1, from about 0.8 toabout 2, from about 0.8 to about 1.7, from about 0.8 to about 1.4, fromabout 0.8 to about 1.2, from about 0.8 to about 1, from about 1 to about2, from about 1 to about 1.7, from about 1 to about 1.4, from about 1 toabout 1.2, from about 1.2 to about 2, from about 1.2 to about 1.7, fromabout 1.2 to about 1.4, from about 1.4 to about 2, from about 1.4 toabout 1.7, etc. The concentrated layer can have a higher water contentto satisfy the water demand of enhancing additives. Since the enhancingadditive content is more concentrated in the concentrated layer in someembodiments, the higher water demand can be more isolated to theconcentrated layer, thereby allowing for a lower WSR in the board core,and, advantageously, a lower water usage overall, particularly in viewof the board core's large contribution to the volume bulk of thecomposite board,

Composite Board Density

The composite gypsum board according to embodiments of the disclosurehas utility in a variety of desired densities for gypsum board, i.e.,dry wall or wallboard (which can encompass such board used not only forwalls but also for ceilings and other locations as understood in theart). As noted herein, board weight is a function of thickness. Sinceboards are commonly made at varying thicknesses (e.g., 3/8 inch, 1/25inch, ¾ inch, one inch, etc,), board density is used herein as a measureof board weight. The advantages of the composite gypsum board inaccordance with embodiments of the disclosure can be seen at a range ofdry densities, including up to heavier board densities, e.g., about 43pcf (about 690 kg/m³) or less, such as from about 18 pcf (about 290kg/m³) to about 43 pcf, from about 20 pcf (about 320 kg/m³) to about 43pcf, from about 20 pcf to about 40 pcf (about 640 kg/m³), from about 24pcf (about 380 kg/m³) to about 43 pcf, from about 27 pcf (about 430kg/m³) to about 43 pcf, from about 20 pcf to about 38 pcf (about 610kg/m³), from about 24 pcf to about 40 pcf, from about 27 pcf to about 40pcf, from about 20 pcf to about 37 pcf (about 600 kg/m³), from about 24pcf to about 37 pcf, from about 2.7 pcf to about 37 pcf, from about 20pcf to about 35 pcf (about 560 kg/m³), from about 24 pcf to about 35pcf, from about 27 pcf to about 35 pcf, etc.

As noted herein, removing solid mass from gypsum wallboard can lead toconsiderable difficulty in compensating for the concomitant loss instrength. Some embodiments of the disclosure surprisingly andunexpectedly enable the use of lower weight board with good strength,lower water demand, and efficient use of enhancing additive. Forexample, in some embodiments, dry board density can be from about 16 pcfto about 33 pcf, e.g., from about 16 pcf to about 27 pcf, from about 16pcf to about 24 pcf, from about18 pcf to about 33 pcf (about 530 kg/m³),from about 18 pcf to about 31 pot from about 18 pcf to about 30 pcf,from about 18 pcf to about 27 pcf, from about 18 pcf to about 24 pa,from about 20 pcf to about 33 pcf from about 20 pcf to about 32 pcf(about 510 kg/m³), from about 20 pcf to about 31 pcf (about 500 kg/m³),from about 20 pcf to about 30 pcf (about 480 kg/m³), from about 20 pcfabout 30 pcf, from about 20 pcf to about 29 pcf (about 460 kg/m³), fromabout 20 pcf to about 28 pcf (about 450 kg/m³), from about 21 pcf (about340 kg/m³) to about 33 pcf, from about 21 pcf to about 32 pcf, fromabout 21 pcf to about 33 pcf, from about 21 pcf to about 32 pcf, fromabout 21 pcf to about 31 pcf, from about 21 pcf to about 30 pcf, fromabout 21 pcf to about 29 pcf, from about 21 pcf to about 28 pcf, fromabout 21 pcf to about 29 pcf, from about 24 pcf to about 33 pcf, fromabout 24 pcf to about 32 pcf, from about 24 pcf to about 31 pcf, fromabout 24 pcf to about 30 pcf, from about 24 pcf to about 29 pcf, fromabout 24 pcf to about 28 pcf, or from about 24 pcf to about 27 pcf.

Composite Board Structure and Assembly

To illustrate an embodiment of the disclosure, reference is made to FIG.1, which shows a schematic cross-sectional view of a composite gypsumboard 10. A face paper 12 serves as a top cover sheet. The face paper 12has a first face 14 and a second face 16. A concentrated layer 18 is inbonding relation to face paper 12. The concentrated layer 18 has a firstface 20 and a second face 22. A board core 24 has a first face 26 and asecond face 28. A back paper 30 serves as a bottom cover sheet, The backpaper 30 has a first face 32 and a second face 34.

As seen in FIG. 1, the composite gypsum board 10 is arranged such thatface 16 of the face paper 12 faces the first face 20 of the concentratedlayer 18 and the second face 22 of the concentrated layer 18 faces thefirst face 26 of the core 24. The second face 28 of the core 24 facesthe first face 32 of the back paper 30.

It will be understood that composite gypsum board in accordance withsome embodiments can be constructed and used in an assembly as will beunderstood in the art. Generally, as will be understood, the compositeboards can be affixed in any suitable arrangement to studs formed of anysuitable material such as wood, metal or the like. The top or face coversheet of the board faces out and is generally decorated (e.g., withpaint, texture, wallpaper, etc.) in use while the bottom or back coversheet faces the studs, A cavity is normally present behind the stud,facing the back paper, in use. If desired, insulation material as knownin the art optionally can be placed in the cavity. In one embodiment,the assembly comprises two composite boards connected by studs with acavity there between, facing the bottom cover sheets of the respectiveboards.

Board Core

The board core forms the majority of the volume of the composite gypsumboard. In some embodiments, the board core forms at least about 60% ofthe board volume, e.g., at least about 70% of the board volume, at leastabout 80% of the board volume, at least about 90% of the board volume,at least about 92%, at least about 95%, at least about 97%, etc. Whilethe concentrated layer has substantial thickness, the board core can beconsiderably thicker. For example, in some embodiments, the dry boardcore can be from about 2,5 times to about 35 times as thick as the dryconcentrated layer, e.g., from about 2.5 times to about 30 times, fromabout 2.5 times to about 25 times, from about 2.5 times to about 20times, from about 2.5 times to about 15 times, from about 2,5 times toabout 10 times, from about 2.5 times to about 5 times, from about 2.8times to about 35 times, from about 2.8 times to about 30 times, fromabout 2.8 times to about 25 times, from about 2.8 times to about 20times, from about 2.8 times to about 15 times, from about 2.8 times toabout 10 times, from about 2,8 times to about 5 times, from about 5times to about 35 times, from about 5 times to about 30 times, fromabout 5 times to about 25 times, from about 5 times to about 20 times,from about 5 times to about 15 times, or from about 5 times to about 10times as thick as the concentrated layer.

In some embodiments, the board core is from about 8 times to about 16times as thick as the concentrated layer, e.g., from about 8 times toabout 12 times, from about 9 times to about 16 times, from about 9 timesto about 14 times, from about 9 times to about 12 times, from about 10times to about 16 times, from about 10 times to about 14 times as thickas the concentrated layer, etc.

The board core is formed from at least water and stucco. As referred toherein throughout, stucco can be in the form of calcium sulfate alphahemihydrate, calcium sulfate beta hemihydrate, and/or calcium sulfateanhydrite. The stucco can be fibrous or non-fibrous. In addition to thestucco and water, the board core is formed from an agent thatcontributes to its lower density, such as a low density filler (e.g.,perlite, low density aggregate or the like), or foaming agents. Variousfoaming agent regimes are well known in the art. Foaming agent can beincluded to form an air void distribution within the continuouscrystalline matrix of set gypsum. In some embodiments, the foaming agentcomprises a major weight portion of unstable component, and a minorweight portion of stable component (e.g., where unstable and blend ofstable/unstable are combined). The weight ratio of unstable component tostable component is effective to form an air void distribution withinthe set gypsum core. See, e.g., U.S. Pat. Nos. 5,643,510; 6,342,284; and6,632,550. In some embodiments, the foaming agent comprises an alkylsulfate surfactant.

Many commercially known foaming agents are available and can be used inaccordance with embodiments of the disclosure, such as the HYONIC line(e.g., 25AS) of soap products from GEO Specialty Chemicals, Ambler, Pa.Other commercially available soaps include the Polystep B25, from StepanCompany, Northfield, Ill. The foaming agents described herein can beused alone or in combination with other foaming agents. The foam can bepregenerated and then added to the stucco slurry. The pregeneration canoccur by inserting air into the aqueous foaming agent. Methods andapparatus for generating foam are well known. See, e.g., U.S. Pat. Nos.4,518,652; 2,080,009; and 2,017,022,

In some embodiments, the foaming agent comprises, consists of orconsists essentially of at least one alkyl sulfate, at least one alkylether sulfate, or any combination thereof but is essentially free of anolefin (e.g., olefin sulfate) and/or alkyne. Essentially free of olefinor alkyne means that the foaming agent contains either (i) 0 wt. % basedon the weight of stucco, or no olefin and/or alkyne, or (ii) anineffective or (iii) an immaterial amount of olefin and/or alkyne. Anexample of an ineffective amount is an amount below the threshold amountto achieve the intended purpose of using olefin and/or alkyne foamingagent, as one of ordinary skill in the art will appreciate. Animmaterial amount may be, e.g., below about 0.001 wt. %, such as belowabout 0.0005 wt. %, below about 0.001 wt. %, below about 0.00001 wt. %,etc., based on the weight of stucco, as one of ordinary skill in the artwill appreciate.

Some types of unstable soaps, in accordance with embodiments of thedisclosure, are alkyl sulfate surfactants with varying chain length andvarying cations. Suitable chain lengths, can be, for example, C₈-C₁₂,e.g., C₈-C₁₀, or C₁₀-C₁₂. Suitable cations include, for example, sodium,ammonium, magnesium, or potassium. Examples of unstable soaps include,for example, sodium dodecyl sulfate, magnesium dodecyl sulfate, sodiumdecyl sulfate, ammonium. dodecyl sulfate, potassium dodecyl sulfate,potassium decyl sulfate, sodium octyl sulfate, magnesium decyl sulfate,ammonium decyl sulfate, blends thereof, and any combination thereof.

Some types of stable soaps, in accordance with embodiments of thedisclosure, are alkoxylated (e.g., ethoxylated) alkyl sulfatesurfactants with varying (generally longer) chain length and varyingcations. Suitable Chain lengths, can be, for example, C₁₀-C₁₄, e.g.,C₁₂-C₁₄, or C₁₀-C₁₂. Suitable cations include, for example, sodium,ammonium, magnesium, or potassium. Examples of stable soaps include, forexample, sodium laureth sulfate, potassium laureth sulfate, magnesiumlaureth sulfate, ammonium laureth sulfate, blends thereof, and anycombination thereof in some embodiments, any combination of stable andunstable soaps from these lists can be used.

Examples of combinations of foaming agents and their addition inpreparation of foamed gypsum products are disclosed in U.S. Pat. No.5,643,510, herein incorporated by reference. For example, a firstfoaming agent which forms a stable foam and a second foaming agent whichforms an unstable foam can be combined. In some embodiments, the firstfoaming agent is a soap, e.g., with an alkoxylated alkyl sulfate soapwith an alkyl chain length of 8-12 carbon atoms and an alkoxy ethoxy)group chain length of 1-4 units. The second foaming agent is optionallyan unalkoxylated (e.g., unethoxylated) alkyl sulfate soap with an alkylchain length of 6-20 carbon atoms, e.g., 6-18 or 6-16 carbon atoms.Regulating the respective amounts of these two soaps, in accordance withsome embodiments, is believed to allow for control of the board foamstructure until about 100% stable soap or about 100% unstable soap isreached.

In some embodiments, a fatty alcohol optionally can be included with thefoaming agent, e.g., in a pre-mix to prepare the foam. This can resultin an improvement in the stability of the foam, thereby allowing bettercontrol of foam (air) void size and distribution. The fatty alcohol canbe any suitable aliphatic fatty alcohol. It will be understood that, asdefined herein throughout, “aliphatic” refers to alkyl, alkenyl, oralkynyl, and can be substituted or unsubstituted, branched orunbranched, and saturated or unsaturated, and in relation to someembodiments, is denoted by the carbon chains set forth herein, e.g.,C_(x)-C_(y), where x and y are integers. The term aliphatic thus alsorefers to chains with heteroatom substitution that preserves thehydrophobicity of the group. The fatty alcohol can be a single compound,or can be a combination of two or more compounds.

In some embodiments, the optional fatty alcohol is a C₆-C₂₀ fattyalcohol (e.g., C₆-C₁₈, C₆-C₁₁₆, C₆-C₁₄, C₆-C_(12,)C₆-C₁₀, C₆-C₈, C₈-C₁₆,C₈-C₁₄, C₈-C₁₂, C₈-C₁₀, C₁₀-C₁₆, C₁₀-C₁₄, C₁₀-C₁₂, C₁₂-C₁₆, C₁₂-C₁₄, orC₁₄-C₁₆ aliphatic fatty alcohol, etc.). Examples include octanol,nonanol, decanol, undecanol, dodecanol, or any combination thereof. TheC₁₀-C₂₀ fatty alcohol comprises a linear or branched C₆-C₂₀ carbon chainand at least one hydroxyl group. The hydroxyl group can be attached atany suitable position on the carbon chain but is preferably at or neareither terminal carbon. In certain embodiments, the hydroxyl group canbe attached at the α-, β-, or γ-position of the carbon chain, forexample, the C₆-C₂₀ fatty alcohol can comprise the following structuralsubunits:

Thus, examples of a desired optional fatty alcohol in accordance withsome embodiments are 1 -dodecanol, 1-undecanol, 1-decanol, 1-nonanol,1-octanol, or any combination thereof.

In some embodiments, the optional foam stabilizing agent comprises thefatty alcohol and is essentially free of fatty acid alkyloamides orcarboxylic acid taurides. In some embodiments, the optional foamstabilizing agent is essentially free of a glycol, although glycols canbe included in some embodiments, e.g., to allow for higher surfactantcontent. Essentially free of any of the aforementioned ingredients meansthat the foam stabilizer contains either (i) 0 wt. % based on the weightof any of these ingredients, or GO an ineffective or (iii) an immaterialamount of any of these ingredients. An example of an ineffective amountis an amount below the threshold amount to achieve the intended purposeof using any of these ingredients, as one of ordinary skill in the artwill appreciate. An immaterial amount may be, e.g., below about 0.0001wt. %, such as below about 0.00005 wt. %, below about 0.00001 wt. %,below about 0.000001 wt. %, etc., based on the weight of stucco, as oneof ordinary skill in the art will appreciate.

It has been found that suitable void distribution and wall thickness(independently) can be effective to enhance strength, especially inlower density board (e.g., below about 35 pcf). See, US 2007/0048490 andUS 2008/0090068. Evaporative water voids, generally having voids ofabout 5 μm or less in diameter, also contribute to the total voiddistribution along with the aforementioned air (foam) voids. In someembodiments, the volume ratio of voids with a pore size eater than about5 microns to the voids with a pore size of about 5 microns or less, isfrom about 0.5:1 to about 9:1, such as, for example, from about 0.7:1 toabout 9:1, from about 0.8:1 to about 9:1, from about 1.4:1 to about 9:1,from about 1.8:1 to about 9:1, from about 2.3:1 to about 9:1, from about0.7:1 to about 6:1, from about 1.4:1 to about 6:1, from about 1.8:1 toabout 6:1, from about 0.7:1 to about 4:1, from about 1.4:1 to about 4:1,from about 1.8:1 to about 4:1, from about 0.5:1 to about 2,3:1, fromabout 0.7:1 to about 2.3:1, from about 0.8:1 to about 2.3:1, from about1.4:1 to about 2.3:1, from about 1.8:1 to about 2.3:1, etc.

As used herein, a void size is calculated from the largest diameter ofan individual void in the core, The largest diameter is the same as theFeret diameter. The largest diameter of each defined void can beobtained from an image of a sample. Images can be taken using anysuitable technique, such as scanning electron microscopy (SEM), whichprovides two-dimensional images. A large number of pore sizes of voidscan be measured in an SEM image, such that the randomness of the crosssections (pores) of the voids can provide the average diameter. Takingmeasurements of voids in multiple images randomly situated throughoutthe core of a sample can improve this calculation. Additionally,building a three-dimensional stereological model of the core based onseveral two-dimensional SEM images can also improve the calculation ofthe void sizes. Another technique is X-ray CT-scanning analysis (XMT),which provides a three-dimensional image. Another technique is opticalmicroscopy, where light contrasting can be used to assist indetermining, e.g., the depth of voids, The voids can be measured eithermanually or by using image analysis software, e.g., imageJ, developed byNIH. One of ordinary skill in the art will appreciate that manualdetermination of void sizes and distribution from the images can bedetermined by visual observation of dimensions of each void. The samplecan be obtained by sectioning a gypsum board.

The foaming agent can be included in the core slurry in any suitableamount, e.g., depending on the desired density. in some embodiments, thefoaming agent is present in the slurry for forming the board core, e.g.,in an amount of less than about 0.5% by weight of the stucco such asabout 0.01% to about 0.5%, about 0.01% to about 0.4%, about 0.01% toabout 0.3%, about 0.01% to about 0.25%, about 0.01% to about 0.2%, about0.01% to about 0.15% , about 0.01% to about 0.1%, about 0.02% to about0.4%, about 0.02% to about 0.3%, about 0.02% to about 0.2%, etc., all byweight of the stucco. Since the concentrated layer has a higher density,the slurry for forming the concentrated layer can be made with less (orno) foam, e.g., in an amount from about 0.0001% to about 0.05% by weightof the stucco, e.g., from about 0.0001% to about 0.025% by weight of thestucco, from about 0.0001% to about 0.02% by weight of the stucco, orfrom about 0.001% to about 0.015% by weight of the stucco.

The fatty alcohol can be present, if included, in the core slurry in anysuitable amount. In some embodiments, the fatty alcohol is present inthe core slurry in an amount of from about 0.0001% to about 0.03% byweight of the stucco, e.g., from about 0.0001% to about 0.025% by weightof the stucco, from about 0.0001% to about 0.02% by weight of thestucco, or from about 0.0001% to about 0.01% by weight of the stucco.Since the concentrated layer slurry can have less or no foam, the fattyalcohol is not required in the concentrated layer, or else can beincluded in a lower amount, such as from about 0.0001% to about 0.004%by weight of the stucco, e.g., from about 0.00001% to about 0.003% byweight of the stucco, from about 0.00001% to about 0.0015% by weight ofthe stucco, or from about 0.00001% to about 0.001% by weight of thestucco.

Enhancing agent for imparting strength properties as described hereincan also optionally be included in the slurry for forming the boardcore. Other ingredients as known in the art can also be included in theboard core slurry, including, for example, accelerators, retarders, etc.Accelerator can be in various forms (e.g., wet gypsum accelerator, heatresistant accelerator, and climate stabilized accelerator). See, e.g.,U.S. Pat. Nos. 3,573,947 and 6,409,825. In some embodiments whereaccelerator and/or retarder are included, the accelerator and/orretarder each can be in the stucco slurry for forming the board core inan amount on a solid basis of such as, from about 0% to about 10% byweight of the stucco (e.g., about 0.1% to about 10%), such as, forexample, from about 0% to about 5% by weight of the stucco (e.g., about0.1% to about 5%).

In addition, the board core and/or concentrated layer can be furtherformed from at least one dispersant to enhance fluidity in someembodiments. The dispersants may be included in a dry form with otherdry ingredients and/or in a liquid form with other liquid ingredients instucco slurry, Examples of dispersants include naphthalenesulfonates,such as polynaphthalenesulfonic acid and its salts(polynaphthalenesulfonates) and derivatives, which are condensationproducts of naphthalenesulfonic acids and formaldehyde; as well aspolycarboxylate dispersants, such as polycarboxylic ethers, for example,PCE211, PCE111, 1641, 1641F, or PCE 2641-Type Dispersants, e.g., MELFLUX2641F, MELFLUX 2651F, MELFLUX 1641F MELFLUX 2500L dispersants (BASF),and COATER Ethacryl M, available from Coatex, Inc.; and/orlignosulfonates or sulfonated lignin. Lignosulfonates are water-solubleanionic polyelectrolyte polymers, byproducts from the production of woodpulp using sulfite pulping. One example of a lignin useful in thepractice of principles of embodiments of the present disclosure isMarasperse C-21 available from Reed Lignin Inc.

Lower molecular weight dispersants are generally preferred. Fornaphthaleneaulfonate dispersants, in some embodiments, they are selectedto have molecular weights from about 3,000 to about 10,000 (e.g., about8,000 to about 10,000). In some embodiments, higher water demandnaphthalenesulfonates can be used, e.g., having molecular weights above10,000, As another illustration, for PCE211 type dispersants, in someembodiments, the molecular weight can be from about 20,000 to about60,000, which exhibit less retardation than dispersants having molecularweight above 60,000.

One example of a naphthalenesulfonate is DILOFLO, available from GEOSpecialty Chemicals. DILOFLO is a 45% naphthalenesulfonate solution inwater, although other aqueous solutions, for example, in the range ofabout 35% to about 55% by weight solids content, are also readilyavailable. Naphthalenesulfonates can be used in dry solid or powderform, such as LOMAR D, available from CEO Specialty Chemicals, forexample. Another example of naphthalenesulfonate is DAXAD, availablefrom GEO Specialty Chemicals, Ambler, Pa.

If included, the dispersant can be provided in any suitable amount. Insome embodiments, for example, the dispersant can be present in theconcentrated layer slurry in an amount, for example, from about 0.05% toabout 0.5%, e.g., about 0.1% to about 0.2% by weight of the stucco, andcan be present in the board core slurry in an amount, for example, fromabout 0% to about 0.7%, e.g., 0% to about 0.4% by weight of the stucco.

In some embodiments, the board core and/or concentrated layer can befurther formed from at least one phosphate-containing compound, ifdesired, to enhance green strength, dimensional stability, and/or sagresistance. For example, phosphate-containing components useful in someembodiments include water-soluble components and can be in the form ofan ion, a salt, or an acid, namely, condensed phosphoric acids, each ofwhich comprises two or more phosphoric acid units; salts or ions ofcondensed phosphates, each of which comprises two or more phosphateunits; and monobasic salts or monovalent ions of orthophosphates as wellas water-soluble acyclic polyphosphate salt. See, e.g., U.S. Pat. Nos.6,342,284; 6,632,550; 6,815,049; and 6,822,033.

Phosphate compositions if added in some embodiments can enhance greenstrength, resistance to permanent deformation (e.g., sag), dimensionalstability, etc. Green strength refers to the strength of the board whilestill wet during manufacture. Due to the rigors of the manufacturingprocess, without sufficient green strength, a board precursor can becomedamaged on a manufacturing line,

Trimetaphosphate compounds can be used, including, for example, sodiumtrimetaphosphate, potassium trimetaphosphate, lithium trimetaphosphate,and ammonium trimetaphosphate. Sodium trimetaphosphate (STMP) ispreferred, although other phosphates may be suitable, including forexample sodium tetrametaphosphate, sodium hexametaphosphate having fromabout 6 to about 27 repeating phosphate units and having the molecularformula Na_(n+2)P_(n)O_(3n+1) wherein n=6−27, tetrapotassiumpyrophosphate having the molecular formula trisodium dipotassiumtripolyphosphate having the molecular formula Na₃K₂P₃O₁₀, sodiumtripolyphosphate having the molecular formula Na₅P₃O₁₀, tetrasodiumpyrophosphate having the molecular formula Na₄P₂O₇, aluminumtrimetaphosphate having the molecular formula Al(PO₃)₃, sodium acidpyrophosphate having the molecular formula Na₂H₂P₂O₇, ammoniumpolyphosphate having 1,000-3,000 repeating phosphate units and havingthe molecular formula (NH₄)_(n+2)P_(n)O_(3n+1) wherein n=1,000−3,000, orpolyphosphoric acid having two or more repeating phosphoric acid unitsand having the molecular formula H_(n+2)PO₃O_(n+1) wherein n is two ormore.

If included, the polyphosphate can be present in any suitable amount. Toillustrate, in some embodiments, the polyphosphate can be present in theconcentrated layer slurry in an amount, for example, from about 0.1% toabout 1%, e.g., about 0.2% to about 0.4% by weight of the stucco, and ispresent in the board core slurry in an amount, for example, from about0% to about 0.5%, e.g., from about 0% to about 0.2% by weight of thestucco. Thus, the dispersant and polyphosphate optionally can be in anysuitable amount in the core slurry and/or in the concentrated layerslurry, such that in some embodiments, the core slurry contains a higherweight percentage of the dispersant and/o polyphosphate than theconcentrated layer slurry. In alternate embodiments, the dispersantand/or polyphosphate are included in higher weight percentage in theconcentrated layer slurry than in the core slurry (including coreslurries with zero dispersant and/or polyphosphate) (with or without theenhancing additive being more concentrated in the concentrated layer).

The board core can have any suitable density useful in contributing to adesired total composite board density, such as, for example, a coredensity of from about 16 pcf (about 260 kg/m³) to about 40 pcf, e.g.,from about 18 pcf to about 40 pcf, 18 pcf to about 38 pcf 18 pcf toabout 36 pcf, 18 pcf to about 32 pct 20 pcf to about 40 pcf, 20 pcf toabout 36 pcf, 20 pcf to about 32 pcf, 22 pcf to about 40 pcf, 22 pcf toabout 36 pcf, 22 pcf to about 32 pcf, 26 pcf to about 40 pcf, 26 pcf toabout 36 pcf, or 26 pcf to about 32 pcf In some embodiments, the boardcore has an even lower density, e.g., about 30 pcf or less, about 29 pcf(about 460 kg/m³) or less, about 28 pcf or less, about 27 pcf (about 430kg/m³) or less, about 26 pcf or less, etc. For example, in someembodiments, the core density is from about 12 pcf (about 190 kg/m³) toabout 30 pcf, from about 14 pcf (about 220 kg/m³) to about 3(1 pcf, 16pcf to about 30 pcf, 16 pcf to about 28 pcf 16 pcf to about 26 pcf, 16pcf to about 22 pcf (about 350 kg/m³), 18 pcf to about 30 pcf, 18 pcf toabout 28 pcf, 18 pcf to about 26 pcf, 18 pcf to about 24 pcf, 20 pcf toabout 30 pcf, 20 pcf to about 28 pcf, 20 pcf to about 26 pcf, 20 pcf toabout 24 pcf, 22 pcf to about 28 pcf, etc.

Concentrated Layer

The concentrated layer is “concentrated” in some embodiments because ofthe presence of an enhancing additive in the concentrated layer slurryin an amount that is more concentrated than the amount by weight, ifany, of the same enhancing additive in the board core slurry. In someembodiments, the concentrated layer has a density that is at least about1.1 times higher than the density of the board core, and/or hassubstantial thickness, such as at least about 0.02 inches (about 0.05cm).

The concentrated layer is formed from slurry comprising water andcementitious material, such as stucco, which hydrates to form a sethydrated material, e.g., continuous crystalline matrix of set gypsum, inthe final product. In preferred embodiments, the cementitious materialis stucco, and the slurry for forming the concentrated layer is a stuccoslurry. As noted, the slurry for forming the concentrated layer furthercomprises an enhancing additive in a higher relative weightconcentration than the concentration of the enhancing additive in theslurry for forming the board core. The slurry for forming theconcentrated layer can optionally include foaming agent or otherlightweight agent as described herein to produce the desired density forthe concentrated layer. If included, in some embodiments the foaming orother lightweight agent will be present in a lower amount in the slurryfor forming the concentrated layer, or the foaming agent can be “beatenout” to at least some extent to reduce the population of foam voids asknown in the art in order to achieve the desired higher density than thedensity of the board core. Thus, the formation of the concentrated layerto the desired density through an effective (or no) amount of foamingagent or other lightweight agent can be achieved as described herein andthrough the ordinary skill in the art. Other ingredients such asaccelerator and retarder can optionally be included in the concentratedlayer as desired as described herein.

Fibers can further be included in the concentrated layer as an optionaladditive to improve the process of preparing gypsum board. In thisregard, as explained herein, the concentrated layer slurry can beapplied to the paper, e.g., at a high rate of speed and with the use ofa roller or other spreading means, which forms a head of slurry thataccumulates upstream of the roller before it is applied evenly to thepaper downstream of the roller (and whereby board edges are typicallyformed around the ends of the roller from the concentrated layerslurry). The environment in which the concentrated layer is applied istransient with three-dimensional oscillation, leading to scalloping inthe slurry, whereby relatively large air entrainments can occur, whichcan cause a rough, uneven slurry that can lead to defects in the boardif not addressed. Such defects can include the formation of large airpockets which are referred to as voids or blisters, as well asdelamination of the paper, soft and/or hard edges, etc.

There are a variety of mechanical and other treatments available foraddressing the scalloping in the flow induced by the unsteadyenvironment in the process, including the use of mechanical pieces tobreak up air pockets as known in the art, such as vibrators on the line,as well as slurry spreaders, various mixer discharge treatments, as wellas formulation adjustments, including water/stucco ratio, viscosity ofthe slurry, etc. However, the inventors have discovered another optionaltechnique, which is the addition of fiber to the concentrated layerslurry as a way to form a smoother slurry, for example, at the headwhere the concentrated layer is applied (e.g., upstream of a roller in apreferred embodiment), with less scalloping and less large air pockets.While not wishing to be bound by any particular theory, it is believedthat the fibers advantageously improve the rheology of the slurry inorder to ensure a smoother flow. It is also believed that the fibersimprove the hydrodynamic properties of the slurry such that viscosity,rheology and the balance of interparticle forces of the slurry areimproved, the slurry is more evenly distributed on the applicationroller, and undesirable entrained air is more easily released from theslurry.

The fibers can be in the form of any suitable fibers, In someembodiments, the fibers can be in the form of one or more of glassfibers, mineral fibers, carbon fibers, paper fibers, and mixtures ofsuch fibers, as well as other comparable fibers providing comparablebenefits to the process and/or end product. In sonic embodiments, glassfibers are incorporated in the concentrated layer slurry and resultingcrystalline core structure. Glass fibers are preferred because they donot absorb water.

In the case of some fibers, such as glass fibers, it can be useful insome embodiments to optionally treat the fibers with sizing agentadditive to improve their properties and handling. For example, sizingagents can allow for sizing of individual fibers in order to, e.g.,change surface coating and properties and typically be in the form ofone or more of organofunctionalized silanes, forming agents,surfactants, defoamers, lubricants and/or stabilizers. As one ofordinary skill in the art will appreciate, the precise selection of eachingredient can vary depending on fiber properties and the desiredapplication. For example, the silanes can be, e.g., amino based, such asfor, example, aminopropyltriethoxysilane oraminoethylaminopropyltrimethoxysilane, vinyl based such as for example,vinyltrimethoxysilane or vinyltriacetoxysilane, alkyl based such asmethyltrimethoxysilane or methyltriethoxysilane, or any combinationthereof.

Forming agents are often polymers and can be hydrophobic to providedesired wetting characteristics and protection from fiber-to-fiberdamage. The forming agents can be in the form of, for example,polyurethanes, polyvinyl acetates, polyesters, polyalkenes and epoxies,Cationic lubricants can optionally be added and can be in the Man ofaliphatic ethanolamides such as stearic ethanolamide, orpolyethyleneimine polyamides, alkylamidoalkyl sultaines or polyethyleneoxide, or any combination thereof Surfactants can optionally be includedto emulsify the forming agent, e.g., when the forming agent ishydrophobic. In some embodiments, the surfactant if included is nonionicor slightly cationic, and can be in the form of an amide or othersuitable form, e.g., polyoxyethylene glycol alkyl esters, copolymers ofpolyethylene glycol and polypropylene glycol, cocamide monoethanolamine,or any combination thereof. Defoamers can provide benefit because theycontrol foam formation with glass fiber, and any suitable defoamer canbe used. For example, suitable defoamers can be siloxane based, oilbased or polymer based, such as, but not limited to mineral oil, waxes,ethylene bis stearainide, silicone oil, polyethylene glycol andpolypropylene glycol copolymers based defoamers, or any combinationthereof Stabilizers provide the benefit of stabilizing the sizingformulation and any suitable stabilizer can be used. In someembodiments, additive such as lubricant provides a positive surfacecharge which is believed to further improve slurry flow.

If included, the sizing agent can be provided in any suitable amount inthe slurry for forming the concentrated layer. For example, the sizingagent can be provided in an amount of from about 0.02 wt. % to about 2wt. % of the fibers, such as from about 0.05 wt. % to about 1 wt. %, orfrom about 0.1 wt. % to about 1.5 wt. % of the fibers. For the weightpercentages of ingredients provided herein in relation to either theboard core slurry or concentrated layer slurry, in some embodiments, theconcentrated layer and/or board core in the board product can containthe recited ingredient in an amount within the recited ranges.

The fibers (e.g., glass fiber) can have any suitable length. Forexample, in some embodiments, the fibers can have an average length offrom about 0.125 inch (about 0.32 cm) to about 1 inch (about 2.54 cm),such as, for example, from about 0.125 inch to about 0.75 inch (about1.9 cm), from about 0.125 inch to about 0.5 inch (about 1.3 cm), fromabout 0.125 inch to about 0.375 inch (about 1 cm), from about 0.125 inchto about 0.25 inch (about 0.6 cm), from about 0.25 inch to about 1 inch,from about 0.25 inch to about 0.75 inch, from about 0.25 inch to about0.5 inch, from about 0.25 inch to about 0.375 inch, from about 0.375inch to about 1 inch, from about 0.375 inch to about 0.75 inch, fromabout 0.375 inch to about 0.5 inch, from about 0.5 inch to about 1 inch,from about 0.5 inch to about 0.75 inch, or from about 0.75 inch to about1 inch.

The fibers (e.g., glass fiber) can have any suitable average diameter.For example, in some embodiments the fibers can have an average diameterof from about 5 microns to about 20 microns, from about 10 microns toabout 15 microns, from about 10 microns to about 20 microns, from about8 microns to about 18 microns, from about 5 microns to about 25 microns,from about 9 microns to about 20 microns, from about 10 microns to about18 microns, from about 7 microns to about 18 microns, from about 10microns to about 25 microns, a diameter of about 11 to about 17 microns,or a diameter of from about 15 microns to about 17 microns.

In some embodiments, such glass fibers can have an average length ofabout 0.5 to about (1675 inches (about 1.7 cm) and a diameter of about13 to about 16 microns, an average length of about 0.5 to about 0.75inches and a diameter of about 11 to about 17 microns, or an averagefiber length of 0.5 inch and an average diameter of from about 15.24microns to about 16.51 microns.

The aspect ratio of the fibers refers to the length divided by thediameter and in practice is believed to influence the slurry flowcharacteristics. To make the units consistent, the length in inches canbe converted into microns such that the values are unitless. In someembodiments, the preferred aspect ratio is from about 200 to about 2000,such as from about 400 to about 1300, e.g., from about 800 to about1500, from about 250 to about 1000, from about 500 to about 1500, orfrom about 700 to about 1600, from about 800 to about 1400.

If included, fibers, such as glass fibers, are present in the slurry forforming the concentrated layer in any suitable amount, such as, fromabout 0.1% to about 3%, e.g., from about 0.13% to about 2.5%, or fromabout 0.5% to about 1% by weight of the stucco, and is present in theboard core in any suitable amount, such as from about 0% to about 1%,e.g., from 0% to about 0.5% by weight of the stucco, If desired, thefiber (and the aforementioned associated additives such as sizing agent,etc) can also be included in the core in any suitable amount such asthese enumerated weight percentages.

The concentrated layer desirably has substantial thickness. In someembodiments, the dry concentrated layer has a substantial thickness ofat least about 0.02 inches (about 0.05 cm), such as from about 0.02inches to about 0.2 inches (about 0.5 cm). For example, in variousembodiments, the concentrated layer has a substantial thickness with aminimum thickness of at least about 0.025 inches (about 0.06 cm), atleast about 0.03 inches (about 0.075 cm), at least about 0.035 inches(about 0.09 cm), at least about 0.04 inches (about 0.1 cm), at leastabout 0.045 inches (about 0.11 cm), at least about 0.05 inches (about0.13 cm), at least about 0.055 inches (about 0.14 cm), at least about0.06 inches (about 0.15 cm), at least about 0.065 inches (about 0.17cm), at least about 0.07 inches (about 0.18 cm), at least about 0.075inches (about 0.19 cm), at least about 0.08 inches (about 0.2 cm), atleast about 0.085 inches (about 0.22 cm), at least about 0.09 inches(about 0.23 cm), at least about 0.095 inches (about 0.24 cm), at leastabout 0.1 inch (about 0.254 cm), at least about 0.11 inch (about 0.28cm), at least about 0.12 inch (about 0.3 cm), at least about 0.13 inch(about 0.33 cm), at least about 0.14 inch (about 0.36 cm), at leastabout 0.15 inch (about 0.38 cm), or at least about 0.16 inch (about 0.41cm); wherein each of these ranges has a suitable upper limit asmathematically appropriate, such as, for example, about 0.2 inches,about 0.185 inches (about 0.47 cm), about 0.175 inches (about 0.45 cm),about 0.16 inches, about 0.15 inches (about 0.38 cm), about 0.145 inches(about 0.37 cm), about 0,13 inches, about 0.12 inches (bout 0.3 cm), 0.1inch, about 0.09 inches (0.23 cm), about 0.08 inches, about 0.07 inches,about 0.06 inches, about 0.055 inches, about 0.05 inches, about 0.045inches, about 0.04 inches, about 0.035 inches, etc.).

To illustrate, but not by way of any limitation, the dry concentratedlayer can have a thickness from about 0.02 inches to about 0.175 inches,e.g., from about 0.02 inches to about 0.15 inches, from about 0.02inches to about 0.12 inches, from about 0.02 inches to about 0.1 inches,from about 0.02 inches to about 0.08 inches, from about 0.02 inches toabout 0.055 inches, from about 0.02 inches to about 0.05 inches, fromabout 0.02 inches to about 0.04 inches, from about 0.02 inches to about0.03 inches, from about 0.03 inches to about 0.2 inches, from about 0.03inches to about 0.175 inches, from about 0.03 inches to about 0.15inches, from about 0.03 inches to about 0.12 inches, from about 0.03inches to about 0.1. inches, from about 0.03 inches to about 0008inches, from about 0.03 inches to about 0.055 inches, from about 0.03inches to about 0.05 inches, from about 0.04 inches to about 0.2 inches,from about 0.04 inches to about 0.175 inches, from about 0.04 inches toabout 0.15 inches, from about 0.04 inches to about 0.12 inches, fromabout 0.04 inches to about 0.1 inches, from about 0.04 inches to about0.08 inches, from about 0.04 inches to about 0.055 inches, from about0.04 inches to about 0.05 inches, from about 0.05 inches to about 0.2inches, from about 0.05 inches to about 0,175 inches, from about 0.05inches to about 0.15 inches, from about 0.05 inches to about 0.12inches, from about 0.05 inches to about 0.1 inches, from about 0.05inches to about 0.8 inches, from about 0.06 inches to about 0.2 inches,from about 0.06 inches to about 0.175 inches, from about 0.06 inches toabout 0.15 inches, from about 0.06 inches to about 0.12 inches, fromabout 0.06 inches to about 0.1 inches, from about 0.06 inches to about0.8 inches, etc.

The concentrated layer preferably has a higher dry density and/or drystrength than the density of the board core. For example, in someembodiments, the concentrated layer has a density that is at least about1.1 times greater than the density of the board core, e.g., at leastabout 1,2 times greater, at least about 1.3 times greater, at leastabout 1.4 times greater, at least about 1.5 times greater, at leastabout 1.6 times greater, at least about 1.7 times greater, at leastabout 1.8 times greater, at least about 1.9 times greater, at leastabout 2 times greater, etc. wherein each of these ranges has a suitableupper limit as mathematically appropriate, such as, for example, about 3times greater, about 2.9 times greater, about 2.8 times greater, about2.7 times greater, about 2.6 times greater, about 2.5 times greater,about 2.4 times greater, about 2.3 times greater, about 2.2 timesgreater, about 2.1 times greater, about 2 times greater, about 1.9 timesgreater, about 1,8 times greater, about 1.7 times greater, about 1.6times greater, about 1.5 times greater, about 1,4 times greater, about1.3 times greater, and about 1.2 times greater.

Thus, for example, the concentrated layer can have a dry density that isfrom about 1.1 to about 3 times the density of the board core, e.g.,from about 1.1 to about 3 times, from about 1.1 to about 2.7 times, fromabout 1.1 to about 2.5 times, from about 1.1 to about 2.2 times, fromabout 1.1 to about 2 times, from about 1.1 to about 1.7 times, fromabout 1.1 to about 1.5 times, from about 1.1 to about 1.4 times, fromabout 1.1 to about 1.3 times, from about 1.2 to about 3 times, fromabout 1.2. to about 2.5 times, from about 1.2 to about 2.2 times, fromabout 1.2 to about 2 times, from about 1.2 to about 1.7 times, fromabout 1.2 to about 1.5 times, from about 1.2 to about 1.4 times, fromabout 1.2 to about 1.3 times, from about 1.3 to about 3 times, fromabout 1.3 to about 2.5 times, from about 1.3 to about 2 times, fromabout 1.3 to about 1.7 times, from about 1.3 to about 1.5 times, fromabout 1.3 to about 1.4 times, from about 1.4 to about 3 times, fromabout 1.4 to about 2.5 times, from about 1.4 to about 2.5 times, fromabout 1.4 to about 2 times, from about 1.4 to about 1.7 times, fromabout 1.4 to about 1.6 times, from about 1.4 to about 1.5 times, fromabout 1.5 to about 3 times, from about 1.5 to about 2.5 times, fromabout 1.5 to about 2 times, from about 1.5 to about 1.8 times, fromabout 1.5 to about 1.7 times, from about 1.5 to about 1.6 times, fromabout 1.6 to about 3 times, from about 1.6 to about 2.5 times, fromabout 1.6 to about 2 times, from about 1.1 to about 1.8 times, fromabout 1,7 to about 3 times, from about 1.7 to about 2.5 times, fromabout 1.7 to about 2.2 times, from about 1.7 to about 2 times, fromabout 1.7 to about 1.9 times, from about 1.8 to about 3 times, fromabout 1.8 to about 2.7 times, from about 1.8 to about 2.5 times, fromabout 1.8 to about 2.2 times, from about 1.8 to about 2 times, fromabout 1.9 to about 3 times, from about 1.9 to about 2.7 times, fromabout 1.9 to about 2.5 times, from about 1.9 to about 2.2 times, fromabout 2 to about 3 times, etc.

The composite gypsum board can be designed to demonstrate any suitabledry density differential between the concentrated layer and the boardcore. In some embodiments, the density differential between theconcentrated layer and the board core can be at least about 8 pcf (about130 kg/m³). For example, in some embodiments, the dry densitydifferential between the concentrated layer and the bonding layer can beat least about 10 pcf, at least about 12 pcf, at least about 14 pcf, atleast about 16 pcf, at least about 18 pcf, at least about 20 pcf, etc.In some embodiments, the density differential between the concentratedlayer and the board core is from about 8 pcf to about 50 pcf, such asabout 8 pcf to about 45 pcf (about 720 kg/m³), about 8 pcf to about 40pcf, about 8 pcf to about 35 pcf 8 pcf to about 30 pcf, about 8 pcf toabout 25 pcf (about 400 kg/m³), about 8 pcf to about 20 pcf, about 8 pcfto about 15 pcf (about 240 kg/m³), about 8 pcf to about 12 pcf, about 10pcf (about 160 kg/m³) to about 50 pcf, about 10 pcf to about 45 pcf,about 10 pcf to about 40 pcf, about 10 pcf to about 35 pcf, about 10 pcfto about 30 pcf, about 10 pcf to about 25 pcf, about 10 pcf to about 20pcf, about 10 pcf to about 15 pcf, about 15 pcf to about 50 pcf (about800 kg/m³), about 15 pcf to about 45 pcf, about 15 pcf to about 40 pcf,about 15 pcf to about 35 pcf, about 15 pcf to about 30 pcf, about 15 pcfto about 25 pcf, about 15 pcf to about 20 pcf, about 20 pcf to about 50pcf, about 20 pcf about 45 pcf, about 20 pcf to about 40 pcf, about 20pcf to about 35 pcf, about 20 pcf to about 30 pcf, about 20 pcf to about25 pa, about 25 pcf to about 35 pcf, about 25 pcf to about 30 pcf, etc.

The concentrated layer can have any suitable dry density to fit withinthe desired parameters of embodiments described herein. In someembodiments, the concentrated layer has a dry density of from about 28pcf to about 70 pcf (about 1120 kg/m³), such as from about 28 pcf toabout 65 pcf (about 1040 kg/m³), from about 28 pcf to about 60 pcf(about 960 kg/m³), from about 28 pcf to about 55 pcf (about 880 kg/m³),from about 28 pcf to about 50 pcf, from about 28 pcf to about 45 pcf,from about 28 pcf to about 40 pcf, from about 28 pcf to about 35 pcf,from about 34 pcf to about 70 pcf, from about 34 pcf to about 65 pcf,from about 34 pcf about 60 pcf, from about 34 pcf to about 55 pcf, fromabout 34 pcf to about 50 pcf, from about 34 pcf to about 45 pcf fromabout 34 pcf to about 40 pcf, from about 38 pcf to about 70 pcf, fromabout 38 pcf to about 65 pcf, from about 38 pcf to about 60 pcf fromabout 38 pcf to about 55 pcf, from about 38 pcf to about 50 pcf, fromabout 38 pcf to about 45 pcf, from about 40 pcf to about 70 pcf, fromabout 40 pa to about 65 pcf, from about 40 pcf to about 60 pcf, fromabout 40 pcf to about 55 pcf, from about 40 pcf to about 50 pcf, fromabout 40 pcf to about 45 pcf, from about 36 pcf to about 38 pcf, etc.

The concentrated layer generally has a dry stiffness value that isgreater than the dry stiffness value of the board core, As noted,Young's modulus of elasticity can be used as a measure of dry stiffnessherein, In some embodiments, the dry concentrated layer has a Young'smodulus that is at least about 1.5 times as high as the Young's modulusof the board core, 2 times as high as the Young's modulus of the boardcore, such as, for example, from about 2 times to about 10 times, fromabout 2 times to about 8 times, from about 2 times to about 6 times,from about 2 times to about 4 times, from about 3 times to about 10times, from about 3 times to about 8 times, from about 3 times to about6 times, from about 3 times to about 5 times, from about 4 times toabout 10 times, from about 4 times to about 8 times, from about 4 timesto about 6 times, from about 5 times to about 10 times, from about 5times to about 8 times, from about 6 times to about 10 times, from about6 times to about 8 times, etc. In some embodiments, the concentratedlayer has a stiffness value that is closer to a stiffness value of thetop and/or bottom cover sheet than a stiffness of the board core, wheneach stiffness value is measured according to Young's modulus. in someembodiments, the concentrated layer has a stiffness value according toYoung's modulus that is from about 0.1 to about 0.5 of the Young'smodulus for at least one of the cover sheets.

Cover Sheets

The cover sheets can be in any suitable form. It will be understoodthat, with respect to cover sheets, the terms “face” and “top” sheetsare used interchangeably herein, while the terms “back” and “bottom” arelikewise used interchangeably herein. For example, the cover sheets maycomprise cellulosic fibers, glass fibers, ceramic fibers, mineral wool,or a combination of the aforementioned materials. One or both of thesheets may comprise individual sheets or multiple sheets. In preferredembodiments, the cover sheets comprise a cellulosic fiber. For example,paper sheet, such as Manila paper or kraft paper, can be used as theback sheet. Useful cover sheet paper includes Manila 7-ply and News-Line3 ply, or 7 ply available from United States Gypsum Corporation,Chicago, Ill.; Grey-Back 3-ply and Manila Ivory 3-ply, available fromInternational Paper, Newport, Ind.; and Manila heavy paper and MH ManilaHT (high tensile) paper, available from United States GypsumCorporation, Chicago, Ill. An exemplary cover sheet paper is 5-plyNewsLine. In some embodiments, the back sheet can optionally defineperforations, e.g., pin-holes, therein. Such perforations assist withdrying in a kiln to provide an outlet for any steam formed during theheating process.

In addition, the paper (e.g., cellulosic) can comprise any othermaterial or combination of materials. For example, one or both sheets,particularly the face (top) sheet can include polyvinyl alcohol, boricacid, or polyphosphate as described herein (e.g., sodiumtrimetaphosphate) to enhance the strength of the paper. In someembodiments, the paper can be contacted with a solution of one or moreof polyvinyl alcohol, boric acid, and/or polyphosphate so that the paperis at least partially wetted. The paper can be at least partiallysaturated in some embodiments. The polyvinyl alcohol, boric acid and/orboric acid can penetrate the fibers in the paper in some embodiments.The solution of polyvinyl alcohol, boric acid, and/or polyphosphate canbe in any suitable amount and can be applied in any suitable manner aswill be appreciated in the art. For example, the solution can be in theform of from about 1% to about 5% solids by weight in water of eachingredient present between the polyvinyl alcohol, the boric acid and/orpolyphosphate, which can be added in one solution or if desired inmultiple solutions.

In some embodiments, one or both sheets can comprise glass fibers,ceramic fibers, mineral wool, or a combination of the aforementionedmaterials. One or both sheets in accordance with the present disclosurecan be generally hydrophilic, meaning that the sheet is at leastpartially capable of adsorbing water molecules onto the surface of thesheet and/or absorbing water molecules into the sheet.

In other embodiments, the cover sheets can be “substantially free” ofglass fibers ceramic fibers, mineral wool, or a mixture thereof, whichmeans that the cover sheets contain either (i) 0 wt. % based on theweight of the sheet, or no such glass fibers ceramic fibers, mineralwool, or a mixture thereof, or (ii) an ineffective or (iii) animmaterial amount of glass fibers ceramic fibers, mineral wool, or amixture thereof. An example of an ineffective amount is an amount belowthe threshold amount to achieve the intended purpose of using glassfibers ceramic fibers, mineral wool, or a mixture thereof, as one ofordinary skill in the art will appreciate. An immaterial amount may be,e.g., below about 5 wt. %, such as below about 2 wt. %, below about 1wt. %, below about 0.5 wt. %, below about 0.2 wt. %, below about 0.1 wt.%, or below about 0.01 wt. % based on the weight stucco as one ofordinary skill in the art will appreciate, However, if desired inalternative embodiments, such ingredients can be included in the coversheets.

In some embodiments, the thermal conductivity of the top and/or bottomsheet is less than about 0.1 w/(m.k.), For example, the thermalconductivity of the top and/or bottom sheet is less than about 0.05w/(m.k.).

If desired, in some embodiments, one or both cover sheets can optionallyinclude any suitable amount of inorganic compound or mixture ofinorganic compounds that adequately imparts greater fire endurance wheresuch properties are sought. Examples of suitable inorganic compoundsinclude aluminum trihydrate and magnesium hydroxide. For example, thecover sheets can comprise any inorganic compound or mixture of inorganiccompounds with high crystallized water content, or any compound thatreleases water upon heating. In some embodiments, the amount ofinorganic compound or the total mixture of inorganic compounds in thesheet ranges from about 0.1% to about 30% by weight of the sheet. Theinorganic compound or inorganic compounds used in the sheet may be ofany suitable particle size or suitable particle size distribution.

Aluminum trihydrate (ATH), also known as alumina trihydrate and hydratedalumina, can increase fire resistance due to its crystallized orcompound water content, In some embodiments, ATH can be added in anamount from about 5% to about 30% by total weight of the sheet. ATHtypically is very stable at room temperature. Above temperatures betweenabout 180° C. and 205° C., ATH typically undergoes an endothermicdecomposition releasing water vapor. The heat of decomposition for suchATH additives is greater than about 1000 Joule/gram, and in oneembodiment is about 1170 Joule/gram. Without being bound by theory, itis believed that the ATH additive decomposes to release approximately35% of the water of crystallization as water vapor when heated above205° C. in accordance with the following equation: Al(OH)₃→Al₂O₃+3H₂O.

A cover sheet comprising inorganic particles of high water content, suchas ATH, can increase fire endurance of the composite board, Theinorganic compound or mixture of compounds is incorporated into thesheet in some embodiments. A cover sheet such as paper comprising ATHcan be prepared by first diluting cellulosic fiber in water at about 1%consistency, then mixing with ATH particles at a predetermined ratio.The mixture can be poured into a mold, the bottom of which can have awire mesh to drain off water. After draining, fiber and ATH particlesare retained on the wire. The wet sheet can be transferred to a blotterpaper and dried at about 200-360° F.

In some embodiments, as described for inclusion in the cover sheet or ina stucco slurry, e.g., ATH particles of less than about 20 μs arepreferred, but any suitable source or grade of ATH can be used. Forexample, ATH can be obtained from commercial suppliers such as Huberunder the brand names SB 432 (10 μm) or Hydral® 710 (1 μm).

in some embodiments, the cover sheet may comprise magnesium hydroxide.In these embodiments, the magnesium hydroxide additive preferably has aheat of decomposition greater than about 1000 Joule/gram, such as about1350 Joule/gram, at or above 180° C. to 205° C. In such embodiments, anysuitable magnesium hydroxide can be used, such as that commerciallyavailable from suppliers, including Akrochem Corp. of Akron, Ohio.

In other embodiments, the cover sheets can be “substantially free” ofinorganic compounds such as ATH, magnesium hydroxide, or a mixturethereof, which means that the cover sheets contain either (i) 0 wt. %based on the weight of the sheet, or no such inorganic compounds such asATH, magnesium hydroxide, or a mixture thereof, or (ii) an ineffectiveor (iii) an immaterial amount of inorganic compounds such as ATH,magnesium hydroxide, or a mixture thereof An example of an ineffectiveamount is an amount below the threshold amount to achieve the intendedpurpose of using inorganic compounds such as ATH, magnesium hydroxide,or a mixture thereof, as one of ordinary skill in the art willappreciate. An immaterial amount may be, e.g., below about 5 wt. %, suchas below about 2 wt. %, below about 1 wt. %, below about 0.5 wt. %,below about 0.1 wt. %, below about 0.05 wt. %, below about 0.01 wt. %,etc.

The cover sheets can also have any suitable total thickness. In someembodiments, at least one of the cover sheets has a relatively highthickness, e.g., a thickness of at least about 0.014 inches. In someembodiments, it is preferred that there is an even higher thickness,e.g., at least about (1.015 inches, at least about 0.016 inches, atleast about 0.017 inches, at least about 0.018 inches, at least about0.019 inches, at least about 0.020 inches, at least about 0.021 inches,at least about 0.022 inches, or at least about 0.023 inches. Anysuitable upper limit for these ranges can be adopted, e.g., an upper endof the range of about 0.030 inches, about 0.027 inches, about 0.025inches, about 0.024 inches, about 0.023 inches, about 0.022 inches,about 0.021 inches, about 0.020 inches, about 0.019 inches, about 0.018inches, etc. The total sheet thickness refers to the sum of thethickness of each sheet attached to the gypsum board.

The cover sheets can have any suitable density. In some embodiments, atleast one of the cover sheets, e.g., the top (face) cover sheet, has adensity that is equal to or greater than the density of the concentratedlayer. For example, in some embodiments, at least one or both of thecover sheets has a density of at least about 36 pcf, e.g., from about 36pcf to about 46 pcf, such as from about 36 pcf to about 44 pcf, fromabout 36 pcf to about 42 pcf, from about 36 pcf to about 40 pcf, fromabout 38 pcf to about 46 pcf, from about 38 pcf to about 44 pcf, fromabout 38 pcf to about 42 pcf, etc.

The cover sheet can have any suitable weight. For example, in someembodiments, lower basis weight cover sheets (e.g., formed from paper)such as, for example, at least about 33 lbs/MSF (about 160 g/m²), e.g.,from about 33 lbs/MSF to about 65 lbs/MSF (about 320 g/m²), from about33 lbs/MSF to about 60 lbs/MSF (about 290 g/m²), 33 lbs/MSF to about 58lbs/MSF (about 280 g/m²), from about 33 lbs/MSF to about 55 lbs/MSF(about 270 g/m²), from about 33 lbs/MSF to about 50 lbs/MST (about 240g/m²), from about 33 lbs/MSF to about 45 lbs/MSF (about 220 g/m²), etc,or less than about 45 lbs/MSF, can be utilized in some embodiments, inother embodiments, one or both cover sheets has a basis weight fromabout 38 lbs/MSF (about 190 g/m²) to about 65 lbs/MSF, from about 38lbs/MSF to about 60 lbs/MSF, from about 38 lbs/MSF to about 58 lbs/MSF,from about 38 lbs/MSF to about 55 lbs/MSF, from about 38 lbs/MSF toabout 50 lbs/MSF, or from about 38 lbs/MSF to about 45 lbs/MSF.

However, if desired, in some embodiments, even heavier basis weights canbe used, to further enhance nail pull resistance or to enhance handling,e.g., to facilitate desirable “feel” characteristics for end-users.Thus, one or both of the cover sheets can have a basis weight of, forexample, at least about 45 lbs/MSF (e.g., from about 45 lbs/MSF to about65 lbs/MSFT, from about 45 lbs/MSF to about 60 lbs/MSF, from about 45lbs/MSF to about 55 lbs/MSF, from about 50 lbs/MSF to about 65 lbs/MSF,from about 50 lbs/MSF to about 60 lbs/MST, etc.), If desired, in someembodiments, one cover sheet (e.g., the “face” paper side wheninstalled) can have the aforementioned higher basis weight, e.g., toenhance nail pull resistance and handling, while the other cover sheet(e.g., the “back” sheet when the board is installed) can have somewhatlower weight basis if desired (e.g., weight basis of less than about 4lbs/MSF, e.g., from about 33 lbs/MSF to about 45 lbs/MSF or from about33 lbs/MSF to about 40 lbs/MSF).

Enhancing Additive

The enhancing additive provides desired strength properties. Inpreferred embodiments, the enhancing additive is more concentrated inthe concentrated layer slurry than in the board core slurry (and/or theresulting layers in the board product), as discussed herein, Examples ofsuitable enhancing additives help provide strength, such as starch,polyvinyl alcohol, boric acid, gypsum-cement, nano-cellulose,micro-cellulose, or any combination thereof The use of the singular termenhancing additive herein is used for convenience but will be understoodto encompass the plural, i,e., more than one enhancing additive incombination, as one of ordinary skill in the art will readilyappreciate. Thus, an enhancing additive may comprise one or more ofstarch, polyvinyl alcohol, boric acid, gypsum-cement, nano-cellulose,and/or micro-cellulose.

In some embodiments, the enhancing additive comprises an ingredient,such as starch, that is effective to increase the dry strength of thecomposite gypsum board relative to the strength of the composite boardwithout the ingredient such as starch (e.g., via increased compressivestrength, nail pull resistance, flexural strength, core hardness, orother strength parameter). With respect to starch, any suitable strengthenhancing starch can be used, including hydroxyalkylated starches suchas hydroxyethylated or hydroxypropylated starch, or a combinationthereof, uncooked starches, or pregelatinized starches, which aregenerally preferred over acid-modifying migrating starches whichgenerally provide paper-core bond enhancement but not core strengthenhancement. However, if desired, the acid-modifying migrating starchcan be included with the enhancing additive in some embodiments.

The starch can be cooked or uncooked. Uncooked starches arecharacterized as being cold water insoluble and having asemi-crystalline structure. Typically, uncooked starches are obtained bywet milling and are not modified by heating wet starch as in the case ofcooked starches. Cooked starches are characterized by being cold watersoluble and having a non-crystalline structure, Cooked starches areprepared by heating wet starch, and can be prepared, e.g., by extrusiontechniques. See, e.g., co-pending U.S. patent applications Ser. No.14/494,547; Ser. No. 14/044,582; and Ser. No. 13/835,002, whichextrusion techniques are incorporated by reference,

Cooked starches are sometimes referred to as pregelatinized starches,because the crystalline structure of the starch granules melts, andresults in starch gelatinization, which is characterized by thedisappearance of the birefringence under a microscope with a polarizedlight Preferred starches, whether cooked or uncooked, are different thanacid-modified migratory starches which do not confer the same strengthproperties and are used in the art for paper-core bond enhancement asthey migrate to the paper-core interface due to their smaller chainlengths, The acid-modified migratory starches have minimal molecularweight, typically below about 6,000 Daltons. In some embodiments,preferred starches in accordance with embodiments of the disclosure havehigher molecular weights, e.g., at least about 30,000 Daltons.

For example, in some embodiments, the starch added to the concentratedlayer slurry can have a molecular weight of from about 30,000 Daltons toabout 150,000,000 Daltons, e.g., from about 30,000 Daltons to about150,000,000 Daltons, from about 30,000 Daltons to about 100,000,000Daltons, from about 30,000 Daltons to about 50,000,000 Daltons, fromabout 30,000 Daltons to about 10,000,000 Daltons, from about 30,000Daltons to about 5,000,000 Daltons, from about 30,000 Daltons to about1,000,000 Daltons, from about 30,000 Daltons to about 500,000 Daltons,from about 30,000 Daltons to about 100,000 Daltons, from about 50,000Daltons to about 150,000,000 Daltons, from about 50,000 Daltons to about100,000,000 Daltons, from about 50,000 Daltons to about 50,000,000Daltons, from about 50,000 Daltons to about 10,000,000 Daltons, fromabout 50,000 Daltons to about 5,000,000 Daltons, from about 50,000Daltons to about 1,000,000 Daltons, from about 50,000 Daltons to about500,000 Daltons, from about 50,000 Daltons to about 100,000 Daltons,from about 100,000 Daltons to about 150,000,000 Daltons, from about100,000 Daltons to about 100,000,000 Daltons, from about 100,000 Daltonsto about 50,000,000 Daltons, from about 100,000 Daltons to about10,000,000 Daltons, from about 100,000 Daltons to about 5,000,000Daltons, from about 100,000 Daltons to about 1,000,000 Daltons, fromabout 100,000 :Daltons to about 500,000 Daltons, or from about 100,000Daltons to about 100,000 Daltons, etc.

Properties of uncooked starches include having low viscosity in coldwater (i.e., at a temperature of 77° F. (25 ° C.)), while properties ofpregelatinized starches include having instant high viscosity in coldwater. Uncooked starches tend to have a viscosity of about 10 centipoiseor less in cold water (e.g., from about I centipoise to about 10centipoise, such as from about 3 centipoise to about 7 centipoise), asmeasured according to a modified rapid viscosity analyzer method. Therapid viscosity analyzer method is explained in the text, Deffenbaugh,L. B. and Walker, C. E., “Comparison of Starch Pasting Properties in theBrabender Viscoamylograph and the Rapid Visco-Analyzer,” CerealChemistry, Vol. 66, No. 6, pp. 493-499 (1989), and modified as definedherein with respect to sample preparation and testing profile asfollows. Starch (20 g, dry) is added into water (180 g) in a Waringblender (model 31BL92) while mixing at low speed for 15 seconds, Starchsolution (28 g) is weighed into a measuring cup. The paddle speed of therapid viscosity analyzer is set at 160 rpm. The testing profile is setwith an initial temperature of 25° C. for 10 min. Heat to 93° C. at aheating rate of 15° C./min. Keep the temperature at 93° C. for 5 min.Cool to 50° C. at a cooling rate of −15° C./min; and keep at 50° C. for1 min. The viscosity value measured at 30 seconds is used as theviscosity of the starch.

The pregelatinized starches have “instant” high viscosity in cold waterbecause the starch tends to instantly dissolve in water. Cooked orpregelatinized starches tend to have a cold water viscosity of at leastabout 100 centipoise (e.g., from about 50 centipoise to about 1000centipoise, such as from about 350 centipoise to about 1000 centipoise)as measured according to the modified rapid viscosity analyzer method.

In some embodiments, uncooked starches are selected because they areeasy to mix with water. This is because of their low viscosity in water.Pregelatinized starches can sometimes cause “fish eye,” which is acondition that is characterized by one or more large lumps that form inthe water solution during mixing. While not wishing to be bound by anyparticular theory, during the mixing process, the large lumps arebelieved to be caused by fast water absorption of the starch, forming aviscous film on the surface of the lump, which prevents waterpenetration of the lump. Uncooked starches are believed to avoid thefish eye condition because of their cold water insolubility, whichresults in the separation of starch granules. However, it will beunderstood that pregelatinized starches can be used in accordance withembodiments of the disclosure inasmuch as they are desirable for theexposure of functional groups which allows for hydrogen bonding betweenstarch and gypsum crystals.

Examples of suitable uncooked starches include, but are not limited to,one or more of native cereal starches, native root starches, nativetuber starches, and/or chemically modified starches, with specificrepresentative examples including, e.g., corn starch (normal, waxy,and/or high-amylose), type wheat starch, B type wheat starch, peastarch, acid modified starches with a molecular weight of at least about30,000 Daltons, substituted starches having substituted groups (such asacetate, phosphate, hydroxyethyl, hydroxypropyl) on starch hydroxylgroups, or any combination thereof In some embodiments, the uncookedstarch excludes pea starch.

Any suitable pregelatinized starch can be included in the enhancingadditive, as described in US 2014/0113124 A1 and US 2015/0010767-A1,which include methods of preparation thereof and desired viscosityranges described therein. If included, the pregelatinized starch canexhibit any suitable viscosity. In some embodiments, the pregelatinizedstarch is a mid-range viscosity starch as measured according to the VMAmethod as known in the art and as set forth in, e.g., US 2014/0113124A1, which VMA method is hereby incorporated by reference.

Desirable pregelatinized starches in accordance with some embodimentscan have a mid-range viscosity, e.g., measured in a 15 wt. % solution ofstarch in water, of from about 20 centipoise to about 700 centipoise,e.g., from about from about 20 centipoise to about 600 centipoise, fromabout 20 centipoise to about 500 centipoise, from about 20 centipoise toabout 400 centipoise, from about 20 centipoise to about 300 centipoise,from about 20 centipoise to about 200 centipoise, from about 20centipoise to about 100 centipoise, from about 30 centipoise to about700 centipoise, from about 30 centipoise to about 600 centipoise, fromabout 30 centipoise to about 500 centipoise, from about 30 centipoise toabout 400 centipoise, from about 30 centipoise to about 300 centipoise,from about 30 centipoise to about 200 centipoise, from about 30centipoise to about 100 centipoise, from about 50 centipoise to about700 centipoise, from about 50 centipoise to about 600 centipoise, fromabout 50 centipoise to about 500 centipoise, from about 50 centipoise toabout 400 centipoise, from about 50 centipoise to about 300 centipoise,from about 50 centipoise to about 200 centipoise, from about 50centipoise to about 100 centipoise, from about 70 centipoise to about700 centipoise, from about 70 centipoise to about 600 centipoise, fromabout 70 centipoise to about 500 centipoise, from about 70 centipoise toabout 400 centipoise, from about 70 centipoise to about 300 centipoise,from about 70 centipoise to about 200 centipoise, from about 70centipoise to about 100 centipoise, from about 100 centipoise to about700 centipoise, from about 100 centipoise to about 600 centipoise, fromabout 100 centipoise to about 500 centipoise, from about 100 centipoiseto about 400 centipoise, from about 100 centipoise to about 300centipoise, from about 100 centipoise to about 200 centipoise, etc.

In accordance with some embodiments, the pregelatinized starch can beprepared as an extruded starch, e.g., where starch is prepared bypregelatinization and acid-modification in one step in an extruder asdescribed in US 2015/0010767-A1, which extrusion method is herebyincorporated by reference. Briefly, any suitable extruder can be used,such as a single-screw extruder (e.g., the Advantage 50 available fromAmerican Extrusion international, located in South Beloit, Ill.) or atwin-screw extruder (e.g., the Wenger TX52 available from Wenger locatedin Sabetha, Kans.). In general, in some embodiments: (a) a precursor topregelatinized starch, i.e., non-pregelatinized starch, (b) an acid inthe form of a weak acid, that substantially avoids chelating calciumions, and/or a strong acid in a small amount, and (c) water, are mixedand fed into the extruder. In some embodiments, additional water may beadded to the extruder. In some embodiments, for example, aluminumsulfate (alum) is an appropriate weak acid to use in preparing the wetstarch since it substantially avoids chelating calcium ions.

For example, in some embodiments, weak acid is included in an amount offrom about 0.5 wt. % to about 5 wt. % based on the weight of the starch.The amount of strong acid is relatively small, such as about 0.05 wt. %or less by weight of the starch, e.g., from about 0.0001 wt. % to about0.05 wt. %. The amounts of strong acid used in accordance with someembodiments of the disclosure are considerably smaller than what wereincluded in conventional systems which used, e.g., at least about 2 g ofsulfuric acid for 35 g of starch. In some embodiments, the strong acidin small amounts as described above can be used in combination with aweak acid that does not chelate calcium ions, such as alum, as describedherein.

While in the extruder, a combination of heating elements and mechanicalshearing melts and pregelatinizes the starch, and the weak acidpartially hydrolyzes the starch to a desired molecular weight indicatedby viscosity as desirable as described herein. For example, the wetstarch can be pregelatinized and acid-modified in an extruder having adie at a temperature of from about 150° C. (about 300° F.) to about 210°C. (about 410° F.). Pressure inside the extruder is determined by theraw material being extruded, moisture content, die temperature, andscrew speed, which will be recognized by one of ordinary skill in theart. For example, the pressure in the extruder can be at least about2,000 psi (about 13,800 kPa), e.g., from about 2,000 psi to about 5,000psi (34,500 kPa), The conditions in the extruder, because of themechanical energy, will also cause the starch molecules to degrade,which partially produces the same effect of acid-modification. It isbelieved that because the conditions in an extruder (e.g., high reactiontemperature and high pressure) in accordance with some embodimentsfacilitate this chemical reaction, a weak acid and/or low amounts of astrong acid can be used.

Cold water solubility relates to a pregelatinized starch having anyamount of solubility in water at room temperature (about 25° C.). Insome embodiments, the pregelatinized starch is partially hydrolyzed andcan have desired cold water solubility of from about 70% to about 100%,from about 75% to about 100%, from about 80% to about 100%, from about85% to about 100%, from about 90% to about 100%, from about 95% to about100%, from about 70% to about 99%, etc., from about 75% to about 99%,from about 80% to about 99%, from about 85% to about 99%, from about 90%to about 99%, from about 95% to about 99%. In some embodiments, thepregelatinized starch has a cold water viscosity (10% solids, 25° C.) offrom about 10 BU to about 120 RU, measured according to the Brabendermethod where viscosity is measured using a C. W. Brabender Viscograph,e.g., a Viscograph-E that uses reaction torque for dynamic measurement.For example, the cold water viscosity can be, e.g., from about 20 BU toabout 110 BU, from about 30 BU to about 100 BU, from about 40 BU toabout 90 BU, from about 50 BU to about 80 BU, or from about 60 BU toabout 70 BU. It is to be noted that, as defined herein, the Brabenderunits are measured using a sample cup size of 16 fl. oz (about 500 cc),with a 700 cmg cartridge at an RPM of 75. One of ordinary skill in theart also will readily recognize that the Brabender units can beconverted to other viscosity measurements, such as centipoises (e.g.,CP=BU×2.1, when the measuring cartridge is 700 cmg) or Krebs units.

In some embodiments, the starch has a cold water viscosity of a 10%slurry of the starch in water when measured at 25 ° C. of from about 60cP to about 160 cP, as measured with a Brookfield viscometer with #2spindle and at a rotation speed of 30 rpm. For example, the cold waterviscosity of a 10% slurry of the starch in water when measured at 25° C.can be from about 60 cP to about 150 cP, from about 60 cP to about 120cP, from about 60 cP to about 100 cP, from about 70 cP to about 150 cP,from about 70 cP to about 120 cP, from about 70 CP to about 100 cP, fromabout 80 cP to about 150 cP from about 80 cP to about 120 cP, from about80 cP to about 100 cP, from about 90 cP to about 150 cP, from about 90cP to about 120 cP, from about 100 cP to about 150 cP, or from about 100cP to about 120 cP.

If included, the starch of any type described herein as enhancingadditive can be present in any suitable amount. In some embodiments, thestarch is present in the concentrated layer in an amount from about 5%to about 40%, by weight of the stucco, e.g., from about 5% to about 35%by weight of the stucco, from about 5% to about 30% by weight of thestucco, from about 5% to about 25%, from about 5% to about 20%, fromabout 5% to about 15%, from about 5% to about 10%, from about 10% toabout 30%, from about 10% to about 25%, from about 10% to about 20%,from about 10% to about 15%, etc. The starch can be present in the boardcore in an amount from about 0% to about 4% by weight of the stucco,e.g., from about 0.1% to about 4% by weight of the stucco, from about0A% to about 3% by weight of the stucco, from about 0.1% to about 2% byweight of the stucco, from about 0.1% to about 1% by weight of thestucco, from about 1% to about 4% by weight of the stucco, from about 1%to about 3% by weight of the stucco, from about 1% to about 2% by weightof the stucco, etc.

In some embodiments, with or without starch, the enhancing additive caninclude polyvinyl alcohol and/or boric acid to enhance strength. In someembodiments, polyvinyl alcohol, boric acid, and starch are all present.While not wishing to be bound by theory, it is believed that the boricacid acts as a cross-linker for the polyvinyl alcohol and starch tofurther enhance starch. In some embodiments, the concentration ofpolyvinyl alcohol and/or boric acid in the concentrated layer isbelieved to positively impact strength in the face paper; this can becompounded by penetrating the face paper with polyvinyl alcohol and/orboric acid as described herein.

If included, the polyvinyl alcohol and boric acid can be present in anysuitable amounts. For example, in some embodiments, the polyvinylalcohol can be present in the concentrated layer in an amount from about1% to about 5% by weight of the stucco, In addition, the polyvinylalcohol can be present in the board core in an amount from about 0% toabout 1% by weight of the stucco. The boric acid can be present in theconcentrated layer in an amount from about 0.1% to about 1% by weight ofthe stucco, and can be present in the board core in an amount from about0% to about 0.1% by weight of the stucco.

In some embodiments, the enhancing additive optionally comprisesnano-cellulose, micro-cellulose, or any combination thereof in order toenhance strength, e.g., nail pull resistance or other strengthparameter. If included, the nano-cellulose, micro-cellulose, orcombination thereof can be present in any suitable amount such as, forexample, in the concentrated layer slurry in an amount, for example,from about 0.01% to about 2%, e.g., from about 0.05% to about 1% byweight of the stucco, and in the board core slurry in an amount, forexample, from about 0% to about 0.5%, e.g., from 0% to about 0.01% byweight of the stucco.

The enhancing additive can comprise gypsum-cement in order to enhancestrength, e.g., nail pull resistance or other strength parameter, insonic embodiments. The gypsum-cement is optional and can be present inany suitable amount. For example, in some embodiments, it can beincluded in the concentrated layer in an amount of from about 5% toabout 30% by weight of the stucco, and can be present in the board corein an amount from about 0% to about 10% by weight of the stucco.

Board Strength

In some embodiments, composite board made according to the disclosuremeets test protocols according to ASTM Standard C473-10. For example, insome embodiments, when the board is cast at a thickness of ½ inch, thedry board has a nail pull resistance of at least about 65 lb_(f) (poundsforce) as determined according to ASTM C473-10 (method B), e.g., atleast about 68 lb_(f), at least about 70 lb_(f), at least about 72lb_(f), at least about 74 lb_(f), at least about 75 lb_(f), at leastabout 76 lb_(f), at least about 77 lb_(f), etc. In various embodiments,the nail pull resistance can be from about 65 lb_(f) to about 100lb_(f), from about 65 lb_(f) to about 95 lb_(f), from about 65 lb_(f) toabout 90 lb_(f), from about 65 lb_(f) to about 85 lb_(f), from about 65lb_(f) to about 80 lb_(f), from about 65 lb_(f) to about 75 lb_(f), fromabout 68 lb_(f) to about 100 lb_(f), from about 68 lb_(f) to about 95lb_(f), from about 68 lb_(f) to about 90 lb_(f), from about 68 lb_(f) toabout 85 lb_(f), from about 68 lb_(f) to about 80 lb_(f), from about 70lb_(f) to about 100 lb;, from about 70 lb_(f) to about 95 lb_(f), fromabout 70 lb_(f) to about 90 lb_(f), from about 70 lb_(f) to about 85lb_(f)from about 70 lb_(f) to about 80 lb_(f), from about 72 lb_(f) toabout 100 lb_(f), from about 72 lb_(f) to about 95 lb_(f), from about 72lb_(f) to about 90 lb_(f), from about 72 lb_(f) to about 85 lb_(f), fromabout 72 lb_(f) to about 80 lb_(f), from about 72 lb_(f) to about 77lb_(f), from about 72 lb_(f) to about 75 lb_(f), from about 75 lb_(f) toabout 100 lb_(f), from about 75 lb_(f) to about 95 lb_(f), from about 75lb_(f) to about 90 lb_(f), from about 75 lb_(f) to about 85 lb_(f), fromabout 75 lb_(f) to about 80 lb_(f), from about 75 lb_(f) to about 77lb_(f), from about 77 lb_(f) to about 100 lb_(f), from about 77 lb₁ toabout 95 lb_(f), from about 77 lb_(f) to about 90 lb_(f), from about 77lb_(f) to about 85 lb_(f), or from about 77 lb₁ to about 80 lb_(f).

In some embodiments, board can have an average core hardness of at leastabout 11 lb_(f), e.g., at least about 12 lb_(f), at least about 13lb_(f), at least about 14 lb_(f), at least about 15 lb_(f), at leastabout 16 lb_(f), at least about 17 lb_(f), at least about 18 lb_(f), atleast about 19 lb_(f), at least about 20 lb_(f), at least about 21lb_(f), or at least about 22 lb_(f), as determined according to ASTMC473-10, method B. In some embodiments, board can have a core hardnessof from about 11 lb_(f) to about 25 lb_(f), e.g., from about 11 lb_(f)to about 22 lb_(f), from about 11 lb_(f) to about 21 lb_(f), from about11 lb_(f) to about 20 lb_(f), from about 11 lb_(f) to about 19 lb_(f),from about 11 lb_(f) to about 18 lb_(f), from about 11 lb_(f) to about 1lb_(f), from about 11 lb_(f) to about 16 lb_(f), from about 11 lb_(f) toabout 15 lb_(f), from about 11 lb_(f) to about 14 lb_(f), from about 11lb_(f) to about 13 lb_(f), from about 11 lb_(f) to about 12 lb_(f), fromabout 12 lb_(f) to about 25 lb_(f), from about 12 lb_(f) to about 22lb_(f), from about 12 lb_(f) to about 21 lb_(f), from about 12 lb_(f) toabout 20lb_(f), from about 12 lb_(f) to about 19 lb_(f), from about 12lb_(f) about 18 lb_(f), from about 12 lb_(f) to about 17 lb_(f), fromabout 12 lb_(f) to about 16 lb_(f) from about 12 lb_(f) to about 15lb_(f), from about 12 lb_(f) to about 14 lb_(r), from about 12 lb_(f) toabout 13 lb_(f), from about 13 lb_(f) to about 25 lb_(f), from about 13lb_(f) to about 22 lb_(f), from about 13 lb_(f) to about 21 lb_(f), fromabout 13 lb_(f) to about 20 lb_(f), from about 13 lb_(f) to about 19lb_(f), from about 13 lb_(f) to about 18 lb_(f), from about 13 lb_(f) toabout 17 lb_(f), from about 13 lb_(f) to about 16 lb_(f), from about 13lb_(f) to about 15 lb_(f), from. about 13 lb_(f) to about 14 lb_(f),from about 14 lb_(f) to about 25 lb_(f), from about 14 lb_(f) to about22 lb_(f), from about 14 lb_(f) to about 21 lb_(f), from about 14 lb_(f)to about 20 lb_(f), from about 14 lb_(f) to about 19 lb_(f), from about14 lb_(f) to about 18 lb_(f), from about 14 lb_(f) to about 17 lb_(f),from about 14 lb_(f) to about 16 lb_(f), from about 14 lb_(f) to about15 lb_(f), from about 15 lb_(f) to about 25 lb_(f), from about 15 lb_(f)to about 22 lb_(f), from about 15 lb_(f) to about 21 lb_(f), from about15 lb_(f) to about 20 lb_(f), from about 15 lb_(f) to about 19 lb_(f),from about 15 lb_(f) to about 18 lb_(f), from about 1 lb_(f) to about 17lb_(f), from about 15 lb_(f) to about 16 lb_(f), from about 16 lb_(f) toabout 25 lb_(f), from about 16 lb_(f) about 22 lb_(f), from about 16lb_(f) to about 21 lb_(f), from about 16 lb_(f) to about 20 lb_(f), fromabout 16 lb_(f) to about 19 lb_(f), from about 16 lb_(f) to about 18lb_(f), from about 16 lb_(f) to about 17 lb_(f), from about 17 lb _(f)to about 25 lb_(f), from about 17 lb_(f) to about 22 lb_(f), from about17 lb_(f) to about 21 lb_(f), from about 17 lb_(f) to about 20 lb_(f),from about 17 lb_(f) to about 19 lb_(f), from about 17 lb_(f) to about18 lb_(f), from about 18 lb_(f) to about 25 lb_(f), from about 18 lb_(f)to about 22 lb_(f), from about 18 lb_(f) to about 21 lb_(f), from about18 lb_(f) to about 20 lb_(f), from about 18 lb_(f) to about 19 lb_(f),from about 19 lb_(f) about 25 lb_(f), from about 19 lb_(f) to about 22lb_(f), from about 19 lb_(f) to about 21 lb_(f), from about 19 lb_(f) toabout 20 lb_(f), from about 21 lb_(f) to about 25 lb_(f), from about 21lb_(f) to about 22 lb_(f), or from about 22 lb_(f) to about 25 lb_(f).

In some embodiments, the concentrated layer has an average dry corehardness that is at least about 1.5 times greater than the average drycore hardness of the board core, wherein the average core hardness ismeasured according to ASTM C-473-10, e.g., at least about 2 timesgreater, 2.5 times greater, 3 times greater, 3.5 times greater, 4 timesgreater, 4.5 times greater, etc., wherein each of these ranges can haveany mathematically appropriate upper limit, such as, for example, 8, 7,6, 5, 4, 3, or 2.

With respect to flexural strength, in some embodiments, when cast in ahoard of V.2 inch thickness, the dry board has a flexural strength of atleast about 36 lb_(f) in a machine direction (e.g., at least about 38lb_(f), at least about 40 lb_(f), etc.) and/or at least about 107 lb_(f)(e.g., at least about 110 lb_(f), at least about 112 lb_(f), etc) in across-machine direction as determined according to the ASTM standardC473-10. In various embodiments, the board can have a flexural strengthin a machine direction of from about 36 lb_(f) to about 60 lb_(f), e.g.,from about 36 lb_(f) to about 55 lb_(f), from about 36 lb_(f) to about50 lb_(f), from about 36 lb_(f) to about 45 lb_(f), from about 36 lb_(f)to about 40 lb_(f), from about 36 lb_(f) to about 38 lb_(f), from about38 lb_(f) to about 60 lb_(f), from about 38 lb_(f) to about 55 lb_(f),from about 38 lb_(f) to about 50 1b₁, from about 38 lb_(f) to about 45lb_(f), from about 38 lb_(f) to about 40 lb_(f), from about 40 lb_(f) toabout 60 lb_(f), from about 40 lb_(f) to about 55 lb_(f), from about 40lb_(f) to about 50 lb_(f), or from about 40 lb_(f) to about 45 lb_(f).In various embodiments, the board can have a flexural strength in across-machine direction of from about 107 lb_(f) to about 130 lb_(f),e.g., from about 107 lb_(f) to about 125 lb_(f), from about 107 lb_(f)to about 120 lb_(f), from about 107 lb_(f) to about 115 lb_(f), fromabout 107 lb_(f) to about 112 lb_(f), from about 107 lb_(f) to about 110lb_(f), from about 110 lb_(f) to about 130 lb_(f), from about 110 lb_(f)to about 125 lb_(f), from about 110 lb_(f) to about 120 lb_(f), fromabout 110 lb_(f) to about 115 lb_(f), from about 110 lb_(f) to about 112lb_(f), from about 112 lb_(f) to about 130 lb_(f), from about 112 lb_(f)to about 125 lb_(f), from about 112 lb_(f) to about 120 lb_(f), or fromabout 112 lb_(f) to about 115 lb_(f).

Advantageously, in various embodiments at various board densities asdescribed herein, the dry gypsum board can have a compressive strengthof at least about 170 psi (1,170 kPa), e.g., from about 170 psi to about1,000 psi (6,900 kPa), from about 170 psi to about 900 psi (6,200 kPa),from about 170 psi to about 800 psi (5,500 kPa), from about 170 psi toabout 700 psi (4,800 kPa), from about 170 psi to about 600 psi (4,100kPa), from about 170 psi to about 500 psi (3,450 kPa), from about 170psi to about 450 psi (3,100 kPa), from about 170 psi to about 400 psi(2,760 kPa), from about 170 psi to about 350 psi (2,41(1 kPa), fromabout 170 psi to about 300 psi (2,070 kPa), or from about 170 psi toabout 250 psi (1,720 kPa). In some embodiments, the board has acompressive strength of at least about 450 psi (3,100 kPa), at leastabout 500 psi (3,450 kPa), at least about 550 psi (3,800 kPa), at leastabout 600 psi (4,100 kPa), at least about 650 psi (4,500 kPa), at leastabout 700 psi (4,800 kPa), at least about 750 psi (5,200 kPa), at leastabout 800 psi (5,500 kPa), at least about 850 psi (5,850 kPa), at leastabout 900 psi (6,200 kPa), at least about 950 psi (6,550 kPa), or atleast about 1,000 psi (6,900 kPa), In addition, in some embodiments, thecompressive strength can be bound by any two of the foregoing points.For example, the compressive strength can be between about 450 psi andabout 1,000 psi (e.g., between about 500 psi and about 900 psi, betweenabout 600 psi and about 800 psi, etc.). The compressive strength can bemeasured using a materials testing system commercially available as ATSmachine model 1610, from Applied Test Systems in Butler, Pa. The load isapplied continuously and without a shock at speed of 1 inch./min.

Due at least in part to the concentrated layer and the benefits thereof,surprisingly and unexpectedly, these standards (e.g., nail pullresistance, flexural strength, and core hardness) can be met even withrespect to ultra light density board (e.g. about 33 pcf or less, such asabout 32 pcf or less, 31 pcf or less, 30 pcf or less, 29 pcf or less, 28pcf or less, 27 pcf or less, 26 pcf or less, etc.), as described herein.Furthermore, these standards surprisingly can be met in some embodimentswhile using less overall enhancing additive and with a lighter, weaker,and/or softer core, and/or with lower overall water usage such thatembodiments of the disclosure provide manufacturing efficiencies.

Process of Preparing Composite Gypsum Board

Composite gypsum board according to embodiments of the disclosure can bemade on typical gypsum wallboard manufacturing lines. For example, boardmanufacturing techniques are described in, for example, U.S. Pat. No.7,364,676 and U.S. Patent Application Publication 2010/0247937, Briefly,the process typically involves discharging a cover sheet onto a movingconveyor, Since gypsum board is normally formed “face down,” this coversheet is the “face” cover sheet in such embodiments.

In accordance with aspects of the disclosure, two separate slurries areformed. One slurry is a stucco slurry used to form the board core, andthe other slurry is used to form the concentrated layer. Theconcentrated layer can be formed from any suitable material, including acementitious material, such as stucco, that hydrates to a set material,e.g., set gypsum. Thus, in various embodiments, slurries containing adesired cementitious material can be prepared. As described herein, insome embodiments where both the board core and the concentrated layerare formed from stucco slurries, the stucco slurry for forming the boardcore can have a lower WSR than the WSR of the stucco slurry used formaking the concentrated layer in seine embodiments.

As noted herein, foaming agent (or other lightweight material) isgenerally more prevalent in the board core slurry to provide its lowerdensity, although some foam or lightweight material can be included inthe concentrated layer slurry so long as the density parameters areachieved, In some embodiments, the concentration of the enhancing agentcan be greater in the concentrated layer and some enhancing agent maynot even be present in the board core slurry in accordance with someembodiments. Accordingly, the feed lines to the respective mixers can beadjusted accordingly, which is well within the level of ordinary skill,

The two slurries can be limited in any suitable manner. For example, twoseparate mixers can be used, where the raw materials are agitated toform the respective slurries. The mixers can be in series orunconnected. Alternatively, one mixer can be used to develop both slurrystreams. FIG. 2 illustrates three alternate schematic flow diagramsshowing examples of how the slurries can be formed in accordance withthe present disclosure. As seen in depiction A of FIG. 2, a single mixercan be used, whereas in depictions B and C, the two slurries are formedin separate mixers, e.g., in the form of “pin mixers” or “pin-lessmixers” as desired. As seen in flow diagrams B and C, if desired forefficiency, the mixer used for the concentrated layer can have a smallermixing volume capacity in some embodiments since the amount of slurryneeded to be applied for the concentrated layer is less than the amountof slurry that is applied to form the board core. The “main” mixer(i.e., for forming the board core slurry) comprises a main body and adischarge conduit (e.g., a gate-canister-boot arrangement as known inthe art, or a modified outlet design (MOD) arrangement as described inU.S. Pat. Nos. 6,494,609 and 6,874,930). As seen in all three depictionsA-C, foaming agent can be added in the discharge conduit of the mixer(e.g., in the gate as described, for example, in U.S. Pat. Nos.5,683,635 and 6,494,609).

Diagram A illustrates an embodiment where the steps occur using onemixer, i.e., the main mixer 100. Stucco 102 and water 104 are insertedinto the main mixer 100, while foam 106 is inserted downstream in thedischarge conduit 108 which can include a modified outlet design orcanister, meaning that foam is not inserted in the body of the mainmixer 100. A portion of the slurry 110, which is essentially foamless,is diverted from the mixer 100 from an exit port, e.g., generally awayfrom the discharge conduit 108 to form the concentrated layer slurry112.

The main mixer 100 acts as a pump to drive the unfoamed slurry 110 outthe smaller discharge port for the concentrated layer slurry which flowsthrough the pressurized slurry line. Additives, particularly, theenhancing additive, in wet form 114 are injected into the pressurizedslurry line through injection ports. The inventors have found that theline is desirably long enough, which can be determined within the levelof ordinary skill, to allow for uniform mixing of slurry includingenhancing additive. There is no need for separate introduction of stuccoor water. As seen in depiction A, edge slurry streams 116 and 118 canalso be diverted from the main mixer 100 without foam so that they havethe desired hardness for their use on the edges as known in the art.

In diagram B, it can be seen that the two mixers 200 and 202 areconnected in series. Stucco 204 and water 206 are added to the mainmixer 200. The foam 208 is added downstream of the body of the mainmixer 200 in the discharge conduit 210 (which can contain a modifiedoutlet design or canister). Thus, foamless slurry 212 can exit the mixer200 through an exit port and inserted into the smaller secondary mixer202 for the concentrated layer, where dry and wet additives 214 (e.g.,via separate lines), including enhancing additive, can be separatelyadded to provide the concentrated effect as desired, Edge slurry streams214 and 216 are also shown as exiting from a port separate from the maindischarge 210 to minimize foam therein and provide their desiredhardness,

In diagram C, it can be seen that there are two mixers 300 and 302 butthe slurries are made separately, with each mixer having its own inputsfor stucco and water as desired. Particularly, stucco 304 and water 306are added into the main mixer 300. Foam 308 is added downstream of thebody of the main mixer 300 in the discharge conduit 310 (which cancontain a canister or modified outlet design as described in U.S. Pat.Nos. 6,494,609 and 6,874,930). Edge slurry streams 312 and 314 can exitfrom a port separate from the main discharge 310 to minimize foamtherein and provide their desired hardness. In a secondary mixer 302 forforming the concentrated layer slurry 316, stucco and water 318, 320 canbe added and mixed. Dry and wet additives (e.g., via separate lines),including enhancing additive as described herein, can be inserted intothe concentrated layer mixer 302. As such, the concentrated layer slurry316 is prepared separately from the core slurry formed in the main mixer300.

In some embodiments, the edge slurries can be extracted from theconcentrated layer mixer, instead of from the main mixer, as desired.The edges can be denser than the board core in some embodiments and,e.g., can have the same density as the concentrated layer. For example,as the concentrated layer is laid down, a portion of the concentratedlayer slurry can flow around the ends of the roller to form edges of theultimate product, as seen in FIGS. 5 and 6 with respect to one end. Thelength of the roller can be configured (e.g., to be shorter than thewidth of the paper) to accommodate the formation of edges in thismanner.

In some embodiments, it will be understood that the discharge conduitcan include a slurry distributor with either a single feed inlet ormultiple feed inlets, such as those described in U.S. Patent ApplicationPublication 2012/0168527 A1 (Application No. 13/341,016) and U.S. PatentApplication Publication 2012/0170403 A1 (application Ser. No.13/341,209), for example. In those embodiments, using a slurrydistributor with multiple feed inlets, the discharge conduit can includea suitable flow splitter, such as those described in U.S. PatentApplication Publication 2012/0170403 A1.

Board is formed in a sandwich structure, normally concurrently andcontinuously, as will be understood in the art, The face cover sheettravels as a continuous ribbon on a conveyor. After being dischargedfrom its mixer, the concentrated layer slurry is applied to the movingface cover sheet. Also, hard edges, as known in the art, can be formed,e.g., from the same slurry stream forming the concentrated layer forconvenience, if desired.

The board core slurry is then applied over the moving face paper bearingthe concentrated layer slurry, and covered with a second cover sheet(typically the “back” cover sheet) to form a wet assembly in the form ofa sandwich structure that is a board precursor to the final product. Theback (bottom) cover sheet may optionally bear a skim coat, which can beformed from the same or different gypsum slurry as for the concentratedlayer. The cover sheets may be formed from paper, fibrous mat or othertype of material (e.g., foil, plastic, glass mat, nonwoven material suchas blend of cellulosic and inorganic filler, etc.). In some embodiments,the concentrated layer is applied on both major sides of the board,i.e., in bonding relation to both the top and bottom sheets.

The wet assembly thereby provided is conveyed to a forming station wherethe product is sized to a desired thickness via forming plate), and toone or more knife sections where it is cut to a desired length. The wetassembly is allowed to harden to form the interlocking crystallinematrix of set gypsum, and excess water is removed using a drying process(e.g., by transporting the assembly through a kiln). Surprisingly andunexpectedly, it has been found that board prepared according to thedisclosure requires significantly less time in a drying process becauseof the low water demand characteristic of the board arrangement andcomposition. This is advantageous because it reduce energy costs.

It also is common in the manufacture of gypsum board to use vibration inorder to eliminate large voids or air pockets from the deposited slurry.Each of the above steps, as well as processes and equipment forperforming such steps, are known in the art.

The following example(s) further illustrate the invention but, ofcourse, should not be construed as in any way limiting its scope.

EXAMPLE 1

This example demonstrates strength characteristics of different types ofhoard samples in accordance with principles of the present disclosure,

In particular, three different boards were tested. Board 1 was acomparative board, absent a concentrated layer. Boards 2 and 3 werecomposite gypsum boards where each contained a concentrated layer andboard core in accordance with principles of the disclosure. Each boardwas prepared at a thickness of about one-half inch with a compositedensity, not including the face and back paper, of about 26 pcf.

Each board was produced as a 6 inch by 6 inch laboratory samplefollowing the general arrangement shown in FIG. 1. Each board containeda face paper having a basis weight of 48 lbs/MST and a back paper havinga basis weight of 42 lbs/MSF (MSF=1000 ft²). The respective thicknessand density for the concentrated layer (if present) and board core foreach board is provided in Tables 1A and 1B.

The enhancing additive was a pregelatinized corn starch having aviscosity of 773 centipoise determined according to the VMA method. InBoards 2 and 3, it can be seen in Tables 1A and 1B that the enhancingadditive was more concentrated in the concentrated layer than in theboard core.

Nail pull resistance was tested in accordance with ASTM 473-10, MethodB. The nail pull values are reported in Table 1C.

TABLE 1A Concentrated Layer (CL) Density % Thickness Board ID (pcf)Starch (in) Board 1 N/A N/A N/A (comparative) Board 2 30 20 0.035 Board3 30 20 0.050

TABLE 1B Board Core Layer (BCL) Board ID Density (pcf) % StarchThickness (in) Board 1 (comparative) 26.0 2 0.467 Board 2 26.0 2 0.467Board 3 26.0 2 0.467

TABLE 1C Composite (CL + BCL) Board ID Density (pcf) Nail Pull (lbf)Board 1 (comparative) 26.0 60.2 Board 2 26.3 70.9 Board 3 26.4 76.3

As can be seen from Table 1C, the comparative sample (Board 1) had a lownail pull resistance value, whereas both of Composite Boards 2 and 3exhibited improved nail resistance. Thus, this Example illustrates thatan improved composite design in accordance with the present disclosureenhances nail pull resistance by incorporating a concentrated layeradjacent to the face paper. This concentrated layer contributes to thedesirable nail pull resistance with a considerable thickness inaccordance with principles of the present disclosure.

EXAMPLE 2

This example demonstrates the effect of various starches on strength ingypsum disks representative of a concentrated layer. Each compositionincluded the ingredients set forth in Table 2, although the type ofstarch varied as shown in Table 3. Particularly, composition 2A was acomparative composition inasmuch as it included no starch. Composition2B included a cooked starch in the form of a pregelatinized starchhaving a viscosity of 80 cP, as measured according to the VMA. Method,as set forth in US 2014/0113124 A1. Compositions 2C-2included one ofvarious uncooked starches as shown in Table 3.

TABLE 2 Wt. % (stucco Ingredients Grams (g) basis) Stucco 300 100 HeatResistance 4.5 1.5 Accelerator Starch 60 20 Sodium 6 0.2Trimetaphosphate (10% solution) Retarder (1% 18 0.06 solution)Dispersant 0.3 0.1 Water 471 165 Total: 859.8 —

The disks were prepared from separate slurry compositions 2A-2O. Incomparative composition 2A, the total weight was 799.8 g as there was nostarch. Each composition was prepared from dry and wet mixes that werecombined. Each wet mix was prepared by weighing the water, dispersant,retarder 1% solution, dispersant, and sodium trimetaphosphate 10%solution in a mixing howl of a Waring blender (model CB15), commerciallyavailable from Conair Corp. (East Windsor, N.J.). The sodiumtrimetaphosphate 10% solution was prepared by dissolving 10 parts(weight) of sodium trimetaphosphate in 90 parts (weight) of water, whilethe retarder 1% solution was composed of an aqueous solution of thepentasodium salt of diethylenetriaminepentaacetic acid (Versenex™ 80,commercially available from DOW Chemical Company, Midland, Mich.), andprepared by mixing 1 part (weight) of Versenex™ 80 with 99 parts(weight) of water. The remaining ingredients, particularly, the stucco,heat resistant accelerator, and starch (if present), were weighed andprepared in a dry mix. The heat resistant accelerator was composed ofground up land plaster and dextrose. The dry mix was poured into theblender with the wet ingredients, and soaked for 5 seconds and thenmixed at high speed for 15 seconds.

Foam was added in order to reduce disk density (and hence weight). Forlb am preparation, a 0.5% solution of Hyonic™ PFM-33 soap (availablefrom GEO Specialty Chemicals, Ambler, Pa.) was formed and then mixedwith air to make the air foam. The air foam was added to the slurryusing a foam generator. The foam generator was operated at a ratesufficient to obtain a density of the final dried disk of 38 pcf.

After foam addition, the slurry was immediately poured into a ring (4″inside diameter and 0.5″ thick) type of mold which was suited forforming a disk sample. The surface of the molds had previously beensprayed with lubricant in the form of WD40™, commercially available fromWD-40 Company, San Diego, Calif. The slurry was poured to a pointslightly above the top of the ring of the molds. The excess slurry wasscraped as soon as the plaster was set. After the disks hardened in themold, the disks were removed from the mold, and heated at 300° F. (149°C.) for 60 min, then dried at 110° F. (43° C.) for about 48 hours untila constant weight was reached. Following removal from the oven, thedisks were allowed to cool at room temperature for one hour. The finaldisks had dimensions of a diameter of 4 inches (10.16 cm), and athickness of 0.5 inches (1.27 cm).

Strength was tested by measuring compressive strength and nail pullresistance. The nail pull resistance was tested in accordance with ASTM473-10, Method B. The compressive strength was measured using thematerials testing system commercially available as SATEC™ E/M Systemsfrom MTS Systems Corp. (Eden Prairie, Minn.). The load was appliedcontinuously and without a shock at speed of 0.04 inch/min (with aconstant rate between 15 to 40 psi/s). The results are shown in Table 3.

TABLE 3 Product Name Compressive Nail Pull Composition Starch(Manufacturer) Strength (psi) (lb_(f)) 2A No Starch N/A 871 (6000 kPa)  78 (350 N) 2B Pregelatinized corn (Bunge North 1549 (10,680 kPa) 161(720 N) flour America, Illinois) 2C A type wheat Midsol 50(MGP 1836(12,660 kPa) 161 (720 N) starch Ingredients, Atchison, KS) 2D A typewheat Manildra 1685 (11,620 kPa) NA* starch 2E B type wheat GemStar 501603 (11,050 kPa) 159 (710 N) starch (Manildra Milling Hamburg, Hamburg,IA) 2F Corn starch GPC Corn, Grain 1306 (9,000 kPa)  NA ProcessingCorporation “GPC,” (Muscatine, IA) 2G Hydroxypropylated K96F (GPC) 1093(7,540 kPa)  NA starch 2H Hydroxypropylated K500F (GPC) 1571 (10,830kPa) NA starch 2I Waxy corn starch Amioca 1664 (11,470 kPa) 197 (880 N)(Ingredion, Inc., Westchester, IL) 2J Regular corn starch Melogel 1520(10,480 kPa) NA (Ingredion) 2K High amylose corn HylonV NA 121 (540 N)starch (Ingredion) 2L Pea starch Tackidex N735 752 (5,180 kPa) NA(Roquette America, Inc. Gurnee, IL,) 2M Acid modified corn Clinton 2771832 (12,630 kPa) 215 (960 N) starch (Archer Daniels Midland “ADM,”Decatur, IL) 2N Acid modified corn Clinton 290 NA 188 (840 N) starch(ADM) 2O Hydroxypropylated Clineo 714 (ADM) 1330 (9,170 kPa)  195 (870N) starch *Values marked with “NA” indicate that the test was not run.

In embodiments where starches are used in the concentrated layer, thisexample illustrates that both cooked and uncooked starches have benefitas enhancing additive for improving strength as shown by the improvementin performance on strength. As seen from Table 3, the uncooked andcooked starches showed considerable improvement in strength over thecomparative composition without the starch, with many of the valuesbeing more than about 50% higher than the strength of the controlwithout starch, more than about 75% higher than the strength of thecontrol without starch, or more than about 100% more than the strengthof the control without starch.

The improvement in strength seen in the disks shown from both cooked anduncooked starches, in accordance with various embodiments of theinvention, indicates the utility of these starches in the concentratedlayer of a gypsum wallboard in accordance with some embodiments becausethe desired starches provides extra bonding between gypsum crystals forstrength improvement. The starches were effective to improve strength,thereby suggesting lack of migration, contrary to the case with amigratory acid-modified starch. Therefore, the example shows that thestarches would be effective in a concentrated layer.

EXAMPLE 3

This example demonstrates the optional use of fibers in the concentratedlayer, In particular, two types of slurries were prepared. Each slurrywas then used to form a concentrated layer in separate production boardsprepared and trialed on the wet end of a manufacturing line. One type ofslurry (composition 3A) did not contain any fiber, while the other typeof slurry (composition 3B) contained glass fiber having a fiber lengthof 0.5 inch (25,400 μm) and diameter of 15.24-16.51 μm, thereby havingan aspect ratio of about 1540 to about 1670 (length divided bydiameter). The glass fiber was in the form of DuraCore™ SF+1/2M300pre-chopped strands, commercially available from Johns Manville Inc.,(Denver, Colo.).

A general representative range of formulation for illustrative purposesonly for the concentrated layer is provided in Table 4, where low andhigh columns are provided to indicate an example of desired ranges ofingredients therebetween (inclusive) in accordance with an embodiment,Other representative formulations and embodiments will be easilyascertained from the full description herein, including the ranges foringredients provided. The trialed formulations are provided in Tables 5Aand 5B, Aside from the differences in glass fiber, the two formulationswere the same, as can be seen in Tables 5A and 5B.

TABLE 4 Low (lbs/MSF) High (lbs/MSF) Stucco 40 200 High wt. % IngredientLow wt. % (stucco basis) (stucco basis) Heat Resistant Accelerator 0.3% 5.0% Pregelatinized Starch 5.0% 60.0% Dispersant 0.0%  2.5% SodiumTrimetaphosphate 0.001%  0.38% Retarder 0.013%  0.250%  Alum 0.00% 0.38% Fiberglass 0.13%  2.50% Dry Density (pcf) Dry Density (pcf)Density 25 65

TABLE 5A Composition 3A Weight Ingredient (lbs/MSF) Wt. % Stucco 8439.96 Heat Resistant 1.88 0.89 Accelerator Pregelatinized 18 8.56 StarchSodium 0.1768 0.08 Trimetaphosphate Retarder 0.02 0.01 Dispersant 0.080.04 Water 106 50.43 Glass fiber 0 0 Total: 210.1568 99.97

TABLE 5B Composition 3B Weight Ingredients (lbs/MSF) Wt. % Stucco 8439.96 Heat Resistant 1.88 0.89 Accelerator Pregelatinized 18 8.56 StarchSodium 0.1768 0.08 Trimetaphosphate Retarder 0.02 0.01 Dispersant 0.080.04 Water 106 50.43 Glass Fiber 0.2 0.10 Total: 210.3568 100.07

The heat resistant accelerator was composed of ground land plaster anddextrose, Each slurry composition was prepared from dry and wetingredients that were combined in a secondary mixer dedicated for theconcentrated layer, separate from the main mixer for preparing the core.The sodium trimetaphosphate, retarder, and dispersant were added inliquid form. The retarder was in the form of pentasodium salt ofdiethylenetriaminepentaacetic acid (Versenex™ 80, commercially availablefrom DOW Chemical Company, Midland, Mich.). The dispersant was in theform of a poly naphthalene sulfonate calcium salt (DURASAR™ commerciallyfrom Ruetgers Polymers, Candiac, Canada). Alum can optionally beincluded to modify the gypsum hydration rate, if desired.

Foam was included in the concentrated layer, and the density of theconcentrated layer produced from both slurries was 36 pcf on a drybasis. For foam preparation, a solution of a mixture of STEOL™ CS230 andPolystep 25 foaming agents (available from Stepan Co., Northfield, Ill.)was formed and then mixed with air to make the air foam using a foamgenerator. The air foam was added to the slurry at the secondary mixer.The amount of foam added was 1% by weight foaming agent. The foamingagent (1% solution) was prepared by dissolving 1 parts (weight) offoaming agent in 100 parts (weight) of water.

In order to prepare trial board on a manufacturing line, paper wasreleased on a continuous roll onto a conveyor as commonly known in theart. The concentrated layer slurry was discharged from the secondarymixer and laid on the paper as it traveled along the conveyor at highspeed (over 600 feet/min). A driven roller was positioned transverse tothe paper and was used to spread the concentrated slurry across thepaper. The roller typically rotates in the direction opposite thedirection the paper travels. The length of the roller was slightly lessthan the width of the paper so that the slurry was allowed to travelaround the ends of the roller over the edges of the paper to ultimatelyform the edges of the finished board product. The roller normally workswith a second roller under the paper with a sufficient gap between therollers to permit the thickness of the paper to travel therebetween.

As the roller obstructs the forward progress of the slurry, a slurryhead forms behind, and just upstream, from the roller, controlledprimarily by tangential speed of the rotating roller. The head is aninventory of slurry that helps decelerate the incoming material,providing spread, which allows for proper amount of slurry to form theconcentrated layer and the edges. The slurry is wiped from the head andcarried by the roller to the downstream side of the roller andre-deposited on the paper and spread to lay what becomes theconcentrated layer of the board, Optionally, a laser can be used tocontrol the head in order to regulate the volume of slurry by varyingthe amount of soap or foam air used which then changes the density ofslurry contained within the head, as known in the art. Downstream, thecore slurry is deposited from the main mixer over the concentrated layerand the board process is completed using understood techniques.

FIGS. 3-6 illustrate images depicting the slurry head (FIGS. 3-4) andthe formation of an edge around the roller (FIGS. 5-6) from themanufacturing trials using the slurries without the glass fiber(composition 3A; FIGS. 3 and 5), and with optional glass fiber(composition 3B; FIGS. 4 and 6). The same trial run using composition 3Awas carried out to illustrate the conditions shown in FIGS. 3 and 5,while the same trial run using composition 3B was carried out toillustrate the conditions shown in FIGS. 4 and 6.

As seen in FIGS. 3-4, the concentrated layer slurry was applied by aroller 400 or 500 to a paper cover sheet 402 or 502. The slurry withoutglass fiber shown in FIG. 3 was deposited on paper 402 upstream ofroller 400 and the deposited slurry traveled toward the roller 400 in aline of slurry 404 that was choppy and uneven. The slurry without glassfiber resulted in a more scalloped slurry head 406, with hydrodynamicinstability 408 resulting in undesired air entrainment. On the otherhand, the slurry with glass fiber shown in FIG. 4 was deposited on paper502 upstream of roller 500 and the deposited slurry traveled in a lineof slurry 504 that was stable and calmer. The slurry with glass fiberresulted in less scalloping and a more even, smooth head 506 with a morestable slurry 508 as a result of a change in rheological properties. Thehead 406 containing scalloping tends to create unstable flow dynamics invarious length and time scales and thereby can result in defects such asvoids, blisters, or paper delamination once the product is kiln dried.

FIG. 5 corresponds with the trial shown in FIG. 3, and FIG. 6corresponds with the trial shown in FIG. 4. Particularly, FIGS. 5-6 showan edge 410 or 510 of the roller 400 or 500. An edge slurry 412 or 512is formed around the edge 410 or 510 of the roller 400 or 500 toultimately form an edge of the board to be produced. The slurry withoutglass fiber resulted in a more variable edge which can cause voids,blisters, paper delamination, soft and/or hard edges, and generaldisruption to the edge formation and manufacturing process, as seen inFIG. 5. As seen in FIG. 5, there is undesirable splashing 414 of theedge slurry over an edge of the paper 402. Due to flow variation, wave416 formation can occur as the slurry is partially lifted onto theroller 400, such that as wave 416 reaches the edge, splashing isundesirably caused. As seen in FIG. 6, the slurry edge 512 is morecontrolled and does not splash over the paper 502. The slurry with glassfiber had less edge variation, resulting in better control, reducing theopportunity for defects such as voids, blisters, paper delamination,soft and/or hard edges, and other disruptions to the manufacturingprocess, as seen in FIG. 6.

It will be appreciated that fiber such as glass fiber is not required inthe concentrated layer. Defects including blisters, voids, delamination,poor edges, etc., can be controlled by other means, including by avariety of mechanical or other means well known in the art. For example,mechanical vibrators can be used under the conveyor to remove large airpockets in the slurry. In addition, other mechanical or other processadjustments will be appreciated, including the use of slurry spreaders,slurry distributors, head control means, and adjustments to mixerdischarge, line speed, and formulation viscosity, etc. These examples ofmechanical and other techniques can be used alone or in combination withglass to provide acceptable results,

EXAMPLES 4-10

In the following Examples 4-10, slurry compositions were prepared asfollows. Each slurry composition was prepared from dry and wetingredients that were combined in a mixer (i.e., a main mixer for thecore slurries, and a secondary mixer dedicated for the concentratedlayer slurries). The water, sodium trimetaphosphate, retarder,dispersant, and alum were added in liquid form. The retarder was in theform of pentasodium salt of diethylenetriaminepentaacetic acid(Versenex™ 80, commercially available from DOW Chemical Company,Midland, Mich.). The dispersant was in the form of a poly naphthalenesultanate calcium salt (DURASAR™ commercially from Ruetgers Polymers,Candiac, Canada). The stucco, heat resistant accelerator, glass fiber,and dextrose were added in solid form. Alum was optionally included tomodify the gypsum hydration rate, if desired. The heat resistantaccelerator was composed of ground land-plaster and dextrose. Additionaldextrose was added in some instances to improve bonding with the back(news-line) paper cover sheet.

Foam was included in the core slurries and concentrated layer slurries.For foam preparation, a solution of a mixture of STEOL™ CS230 andPolystep 25 foaming agent (available from Stepan Co., Northfield, Ill.)was formed and then mixed with air to make the air foam using a foamgenerator. The air foam density was approximately 4.5 lbs per cubicfoot. The air foam was added to core slurry in a discharge conduit ofthe main mixer and added to the concentrated slurry at the secondarymixer. The weight percentage of a specific ingredient is based on itsown weight, versus the total composition of the wet slurry (thus,excluding paper). Any inconsistencies in the totals are due to roundingof values of individual ingredients, e.g., due to effective limits offreadings from equipment such as pumps and flow meters, as will beunderstood by those skilled in the art.

EXAMPLE 4

This example demonstrates a benefit of including a concentrated layer ingypsum board. The example shows that the concentrated layer enhancesnail pull performance. Two boards were prepared, Board 4A and Board 4B.Board 4A did not contain a concentrated layer, Board 4 B did. The slurrycompositions for preparing boards 4A and 4B are set forth in Tables 6and 7, respectively.

TABLE 6 Composition for Board 4A Core Concentrated Layer Weight WeightIngredient (lbs/MSF) Wt. % (lbs/MSF) Wt. % Stucco 996 52.75%  N/A N/AHeat Resistant 17.5 0.93% N/A N/A Accelerator Foaming Agent 0.78 0.04%N/A N/A Pregelatinized 15 0.79% N/A N/A Starch Sodium 1.07 0.06% N/A N/ATrimetaphosphate Retarder 0.46 0.02% N/A N/A Dispersant 0.8 0.04% N/AN/A Alum 0.8 0.04% N/A N/A Glass fiber 0 0.00% N/A N/A Dextrose 1 0.05%N/A N/A Water 854.8 45.27%  N/A N/A Total: 1888  100% N/A N/A

TABLE 7 Composition for Board 4B Core Concentrated Layer Weight WeightIngredients (lbs/MSF) Wt. % (lbs/MSF) Wt. % Stucco 896.3   54% 99.7  41% Heat Resistant 17.5   1% 1.95   1% Accelerator Foaming Agent 0.780.05% 0.04 0.02% Pregelatinized 13.5   1% 14.5   6% Starch Sodium 1.070.06% 0.10 0.04% Trimetaphosphate Retarder 0.46 0.03% 0.04 0.01%Dispersant 0.8 0.05% 0.16 0.07% Alum 0.8 0.05% 0.04 0.01% Glass Fiber 0  0% 0   0% Dextrose 1 0.06% 0.11 0.05% Water 729.7   44% 125.1   52%Total: 1662  100% 242  100%

Boards 4A and 4B were each prepared on a high speed (over 600 ft/min)board manufacturing line (machine) using a main pin mixer to combine wetand dry ingredients in a continuous process to form a continuous ribbonof board precursor, with a core slurry deposited between two sheets ofpaper, as described in Example 3. The concentrated layer was used inpreparing Board 4B with the aid of a secondary board mixer to blend wetand dry ingredients. This concentrated layer slurry was applied to theface paper using an application roller, with the core slurry depositedthereon from a discharge conduit from the main mixer. The precursorswere processed and kiln dried to form the final Boards, 4A and 4B,Properties and dimensions of the hoards are set forth in. Table 8.

TABLE 8 Overall Board Details Concentrated Nail Pull Layer Details BoardBoard Result Formulated Dry Thickness Weight (lbs Thickness DensityBoard (in) (lbs/MSF) force) (in) (pcf) Board 4A 0.5 1290 82.8 N/A N/ABoard 4B 0.5 1289 86.9 0.025 39.4

This example shows a benefit of the concentrated layer in enhancingstrength of the board product. As seen in Table 8, Board 4B, whichincluded the concentrated layer, resulted in an increased nail pull(resistance) value. It will be understood that the term “nail pull”herein refers to nail pull resistance as measured according to ASTM473-10 Method B, unless otherwise stated. Such nail pull improvement isbeneficial in providing strength and enhancing performance in the fieldof the board. Advantageously, increasing nail pull with the aid ofconcentrated layer can be used to reduce board weight and the cost ofmanufacturing wallboard products.

EXAMPLE 5

This example demonstrates a benefit of using a concentrated layer ingypsum board. In particular, tailoring ingredients in the slurry forforming the concentrated layer can be beneficial. The rate in which aconcentrated layer stiffens can be optionally modulated to effect thewashout of the concentrated layer as the main (core) slurry meets theconcentrated layer slurry during the board manufacturing process.Washout refers to the removal of the concentrated layer which can occurwhen the core slurry is distributed over the concentrated layer duringthe continuous manufacturing process. Washout undesirably can result inproduct non-uniformity and reduced nail pull. Two boards were prepared,Boards 5A and 5B. The compositions for preparing Boards 5A and 5B areset forth in Tables 9 and 10, respectively.

The stiffening rate of stucco slurry (sometimes called gypsum slurry) inthis example was modified using alum and retarder. The amount of alumwas decreased in Board 5B to decrease the rate of setting, whileretarder was added to Board 5B to also decrease the rate of setting.

TABLE 9 Composition for Board 5A Core Concentrated Layer Weight WeightIngredient (lbs/MSF) Wt. % (lbs/MSF) Wt. % Stucco 795   55% 84.6 38.06% Heat Resistant 18.6   1% 1.86 0.84% Accelerator Foaming Agent 0.93 0.06%0.046 0.02% Pregelatinized 18 1.25% 20 9.00% Starch Sodium 2.14 0.15%0.18 0.08% Trimetaphosphate Retarder 0.48 0.03% 0.02 0.01% Dispersant2.2 0.15% 0.08 0.04% Alum 0.8 0.06% 0.06 0.03% Glass fiber 0   0% 00.00% Dextrose 1.2 0.08% 0.12 0.05% Water 601   42% 115.3 51.87%  Total:1440  100% 222  100%

TABLE 10 Composition for Board 5B Core Concentrated Layer Weight WeightIngredients (lbs/MSF) Wt. % (lbs/MSF) Wt. % Stucco 795   55% 84.6   38%Heat Resistant 18.6 1.29% 1.86 0.84% Accelerator Foaming Agent 0.930.06% 0.046 0.02% Pregelatinized 18 1.25% 20 9.00% Starch Sodium 2.140.15% 0.18 0.08% Trimetaphosphate Retarder 0.48 0.03% 0.03 0.01%Dispersant 2.2 0.15% 0.08 0.04% Alum 0.8 0.06% 0.04 0.02% Glass Fiber 00.00% 0 0.00% Dextrose 1.2 0.08% 0.12 0.05% Water 601 41.73%  115.3  52% Total: 1440  100% 222  100%

Boards 5A and Mix 5B were each prepared on a high speed machine using amain pin mixer to combine wet and dry ingredients in a continuousprocess, as described in Example 3, to form a continuous ribbon of boardprecursor, with core slurry deposited between two sheets of paper. Aconcentrated layer was used to prepare Boards 5A and 5B with the aid ofa secondary hoard mixer to blend wet and dry ingredients. Thisconcentrated layer slurry was applied to the face paper using anapplication roller, with the core slurry deposited thereon from adischarge conduit from the main mixer. The precursors were processed andkiln dried to form the final hoards 5A and 5B. Properties and dimensionsof the hoards are set forth in Table 11.

Washout was measured utilizing a density profilimeter machine whichutilizes technology (i.e., QDP-01X Density Profiler, commerciallyavailable from Quintek Measurement Systems, Inc., Knoxville, Tenn.) todetermine the density gradient throughout the sample. One inch samplestaken from Boards 5A and 5B were prepared and cut in the cross directionof the board so a density profile could be assembled to represent theentire width and thickness of each board.

TABLE 11 Concentrated Overall Board Details Layer Details Board BoardFormulated Stiffening Thickness Weight Washout Thickness Rate Board (in)(lbs/MSF) (in) (in) (seconds) Board 5A 0.5 1117 0.01 0.025 15-17 Board5B 0.5 1134 0.02 0.025 28-32

This example shows a benefit of using a concentrated layer, as bothBoards 5A and 5B were effective, Board 5A was more preferred because itexhibited less washout. Reducing the stiffening rate led to morepreferred board. As seen in Table 11, Board 5A demonstrated an increasedability to resist washout from the main slurry from contacting theconcentrated layer during the manufacturing process as compared withBoard 5B. In this regard, Board 5A differed from Board 5B in that Board5A was prepared using less retarder and more alum resulting in lesswashout, while Board 5B was prepared using more retarder but includedless alum. The results shown in Table 11 indicate a 50% reduction inwashout for Board 5A as compared with Board 5B, although both boardswere useful products.

EXAMPLE 6

This example demonstrates a benefit of including a concentrated layer ina gypsum board. Particularly, the slurry composition for forming theconcentrated layer can be tailored to include enhancing additives. Asthis example shows, starch concentration can be used to decrease thewashout of the concentrated layer as the main (core) slurry meets theconcentrated layer slurry during the board manufacturing process. Twoboards were prepared, Boards 6A and 6B. The slurry compositions forpreparing Boards 6A and 6B are set forth in Tables 12 and 13,respectively.

TABLE 12 Composition for Board 6A Core Concentrated Layer Weight WeightIngredient (lbs/MSF) Wt. % (lbs/MSF) Wt. % Stucco 795 55.1% 84.6 38.1%Heat Resistant 18.6 1.29% 1.86 0.84% Accelerator Foaming Agent 0.930.06% 0.046 0.02% Pregelatinized 18  1.4% 20  9.0% Starch Sodium 2.140.15% 0.18 0.08% Trimetaphosphate Retarder 0.48 0.03% 0.03 0.01%Dispersant 2.2 0.15% 0.08 0.04% Alum 0.8 0.06% 0.04 0.02% Glass fiber 0  0% 0 0.00% Dextrose 1.2 0.08% 0.12 0.05% Water 601 41.7% 115.3 51.9%Total: 1440  100% 222.3  100%

TABLE 13 Composition for Board 6B Core Concentrated Layer Weight WeightIngredients (lbs/MSF) Wt. % (lbs/MSF) Wt. % Stucco 795 55.2% 84.6 36.2%Heat Resistant 18.6 1.29% 1.86  0.8% Accelerator Foaming Agent 0.930.06% 0.046 0.02% Pregelatinized 18 1.25% 26 11.1% Starch Sodium 2.140.15% 0.18 0.08% Trimetaphosphate Retarder 0.48 0.03% 0.03 0.01%Dispersant 2.2 0.15% 0.08 0.03% Alum 0.8 0.06% 0.04 0.02% Glass Fiber0.000 0.00% 0.0 0.00% Dextrose 1.2 0.08% 0.12 0.05% Water 601 41.7% 121  52% Total: 1440  100% 234  100%

Boards 6A and 6B were each prepared on a high speed machine using a mainpin mixer to combine wet and dry ingredients in a continuous process, asdescribed in Example 3, to form a continuous ribbon of board precursor,with core slurry deposited between two sheets of paper. A concentratedlayer was used to prepare Boards 6A and 6B with the aid of a secondaryboard mixer to blend wet and dry ingredients. This concentrated layerslurry was applied to the face paper using an application roller, withthe core slurry deposited thereon from a discharge conduit from the mainmixer. The precursors were processed and kiln dried to form the finalBoards, 6A and 6B. Properties of the hoards are set forth in Table 14.Washout was measured as described in Example 5.

TABLE 14 Concentrated Overall Board Details Layer Details Board BoardFormulated Stiffening Thickness Weight Washout Thickness Rate Board (in)(lbs/MSF) (in) (in) (seconds) Board 6A 0.5 1134 0.02 0.025 28-32 Board6B 0.5 1145 0.005 0.025 28-32

This example illustrates a benefit of having a concentrated layer.Particularly, it can be seen that haying a higher concentration ofpregelatinized starch in the concentrated layer slurry, as compared withthe core slurry, was beneficial. As seen in Table 14, Board 6Ademonstrated more washout as compared with Board 6B. In this regard,Board 6A differed from Board 6B in that Board 6A was prepared using lesspregelatinized starch, resulting in more washout, while Board 6Bincluded more pregelantinized starch in the slurry. The results shown inTable 14 indicate washout was reduced by 75% in Board 6B as comparedwith Board 6A. Use of more enhancing additive, e.g., pregelatinizedstarch, in the concentrated layer can be less costly and more efficientas the additive is more highly located where the most benefit is seen,i.e., in the concentrated layer.

EXAMPLE 7

This example demonstrates a benefit of including a concentrated layer ina gypsum board. In particular, it is shown that density of aconcentrated layer can be used to improve nail pull. Density wasmodified by changing the amount of foam contained in the concentratedlayer. Two boards were prepared, Boards 7A and 7B. The slurrycompositions for preparing Boards 7A and 7B are set forth in Tables 15and 16, respectively.

TABLE 15 Composition for Board 7A Core Concentrated Layer Weight WeightIngredient (lbs/MSF) Wt. % (lbs/MSF) Wt. % Stucco 789   55% 85 38.7%Heat Resistant 20.5 1.42% 2.05 0.93% Accelerator Foaming Agent 0.920.06% 0.092 0.04% Pregelatinized 18 1.24% 18  8.2% Starch Sodium 2.140.15% 0.18 0.08% Trimetaphosphate Retarder 0.48 0.03% 0.02 0.01%Dispersant 2 0.14% 0.08 0.04% Alum 0.8 0.06% 0.045 0.045%  Glass fiber 20.14% 0.2 0.09% Dextrose 1.2 0.08% 0.12 0.05% Water 609 42.12%  113.751.8% Total: 1446  100% 219.5  100%

TABLE 16 Composition for Board 7B Core Concentrated Layer Weight WeightIngredients (lbs/MSF) Wt. % (lbs/MSF) Wt. % Stucco 789   55% 85   39%Heat Resistant 20.5 1.42% 2.05 0.93% Accelerator Foaming Agent 0.9150.06% 0.046 0.02% Pregelatinized 18 1.24% 18 8.20% Starch Sodium 2.140.15% 0.18 0.08% Trimetaphosphate Retarder 0.48 0.03% 0.02 0.01%Dispersant 2 0.14% 0.08 0.04% Alum 0.8 0.06% 0.045 0.02% Glass Fiber 20.14% 0.2 0.09% Dextrose 1.2 0.08% 0.12 0.05% Water 610.6 42.18%  113.7  52% Total: 1448  100% 219  100%

Boards 7A and 7B were each prepared on a high speed machine using a mainpin mixer to combine wet and dry ingredients in a continuous process, asdescribed in Example 3, to form a continuous ribbon of board precursor,with core slurry deposited between two sheets of paper. A concentratedlayer was used to prepare Boards 7A and 7B with the aid of a secondaryboard mixer to blend wet and dry ingredients. This concentrated layerslurry was applied to the face paper using an application roller, withthe core slurry deposited thereon from a discharge from the main mixer.The precursors were processed and kiln dried to form the final boards7.A and 7B. Properties and dimensions of the boards are set forth inTablet 17.

TABLE 17 Concentrated Overall Board Details Layer Details Board BoardNail Pull Formulated Wet Thickness Weight Result Thickness Density Board(in) (lbs/MSF) (lbs force) (in) (pcf) Board 7A 0.5 1094 66.1 0.025 69Board 7B 0.5 1084 68.3 0.025 75

This example shows benefit and efficiency of using a concentrated layer.Focusing strength additive and density in the concentrated layerprovides an overall strength benefit efficiently. Both boards exhibitedeffective nail pull. As seen in Table 17, Board 7A demonstrateddecreased nail pull as compared with Board 7B. In this regard, Board 7Adiffered from Board 7B in that Board 7A was prepared using more foamingagent in the concentrated layer slurry, resulting in lower density,while Board 7B included less foam in the concentrated layer slurry,resulting in higher density. But the results were similar as Board 7Bwas prepared with a higher weight percentage of starch. The resultsshown in Table 17 indicate that concentrating increased density in theconcentrated layer and increasing enhancing additive dosage (by weightpercentage) in the concentrated layer slurry are effective at increasingnail pull in an efficient manner.

EXAMPLE 8

This example demonstrates a benefit of including a concentrated layer ingypsum board. Starch concentration in the concentrated layer can be usedto improve nail pull. Two boards were prepared, Boards 8A and 8B. Inthis instance, since washout was more prevalent under test conditions,the nail pull difference was measured along the machine direction sideof the board (the non-code side) where washout was not prevalent. Theslurry compositions for preparing Boards 8A and 8B are set forth inTables 18 and 19, respectively.

TABLE 18 Composition for Board 8A Core Concentrated Layer Weight WeightIngredient (lbs/MSF) Wt. % (lbs/MSF) Wt. % Stucco 794   55% 94 38.02% Heat Resistant 20.8 1.45% 2.08 0.84% Accelerator Foaming Agent 0.960.07% 0.048 0.02% Pregelatinized 18 1.26% 20  8.1% Starch Sodium 2.140.15% 0.18 0.73% Trimetaphosphate Retarder 0.48 0.03% 0.02 0.01%Dispersant 2.2 0.15% 0.09 0.04% Alum 1 0.07% 0.07 0.03% Glass fiber 00.00% 0 0.00% Dextrose 1.5 0.10% 0.15 0.06% Water 590.8 41.26%  12952.2% Total: 1432  100% 247  100%

TABLE 19 Composition for Board 8B Core Concentrated Layer Weight WeightIngredients (lbs/MSF) Wt. % (lbs/MSF) Wt. % Stucco 794   55% 94 34.7%Heat Resistant 20.8 1.45% 2.08 0.77% Accelerator Foaming Agent 0.960.07% 0.048 0.02% Pregelatinized 18 1.26% 26 9.61% Starch Sodium 2.140.15% 0.18 0.07% Trimetaphosphate Retarder 0.48 0.03% 0.02 0.01%Dispersant 2.2 0.15% 0.09 0.03% Alum 1 0.07% 0.07 0.03% Glass Fiber 00.00% 0.0 0.00% Dextrose 1.5 0.10% 0.15 0.06% Water 590.8 41.26%  14854.7% Total: 1432  100% 271  100%

Boards 8A and 8B were each prepared on a high speed machine using a mainpin mixer to combine wet and dry ingredients in a continuous process, asdescribed in Example 3, to form a continuous ribbon of hoard precursor,with core slurry deposited between two sheets of paper. A concentratedlayer was used to prepare Boards 8A and 8B with the aid of a secondaryboard mixer to blend wet and dry ingredients. This concentrated Layerslurry was applied to the face paper using an application roller, withthe core slurry deposited thereon from a discharge conduit from the mainmixer. The precursors were processed and kiln dried to form the finalBoards 8A and 8B. Properties and dimensions of the boards are set forthin Table 20.

TABLE 20 Concentrated Overall Board Details Layer Details Board BoardNail Pull Formulated Dry Thickness Weight Result Thickness Density Board(in) (lbs/MSF) (lbs force) (in) (pcf) Board 8A 0.5 1100 77.7 0.035 43.5Board 8B 0.5 1114 82.3 0.035 39.6

This example shows a benefit of using a concentrated layer. Both boardsdemonstrated good nail pull with higher concentration of starch in theconcentrated layer. Adding a higher concentration of pregelatinizedstarch in the concentrated layer resulted in better strength. As seen inTable 20, Board 8A demonstrated lower nail pull as compared with Board8B. In this regard, Board 8A differed from Board 8B in that theconcentrated layer of Board 8A was prepared using less pregelatinizedstarch, resulting in lower nail pull, while the concentrated. layerslurry of Board 8B included more starch, resulting in higher nail pull,The results shown in Table 20 indicate starch concentration in theconcentrated layer can be used to modify the nail pull result.

EXAMPLE 9

This example illustrates a benefit of including a concentrated layer ingypsum hoard. Representative thickness of the concentrated layer forachieving improved nail pull is shown, Other thickness as describedthroughout herein can be used. Two boards were prepared, Boards 9A and9B. Thickness was modified by increasing the speed of the applicationroller and narrowing the spread of the concentrated layer, therebymaking it thicker. The compositions used in preparing 9A and 9B are setforth in Tables 21 and 22, respectively.

TABLE 21 Composition for Board 9A Core Concentrated Layer Weight WeightIngredient (lbs/MSF) Wt. % (lbs/MSF) Wt. % Stucco 793   55% 92.9 38.5%Heat Resistant 20 1.40% 1.5 0.62% Accelerator Foaming Agent 0.95 0.07%0.048 0.02% Pregelatinized 18 1.26% 20  8.3% Starch Sodium 2.14 0.15%0.27 0.11% Trimetaphosphate Retarder 0.48 0.03% 0.025 0.01% Dispersant2.4 0.17% 0.09 0.04% Alum 0.8 0.06% 0.052 0.02% Glass fiber 2 0.14% 0.20.08% Dextrose 1.2 0.08% 0.12 0.05% Water 591 41.27%  126 52.2% Total:1432  100% 241  100%

TABLE 22 Composition for Board 9B Core Concentrated Layer Weight WeightIngredients (lbs/MSF) Wt. % (lbs/MSF) Wt. % Stucco 793   55% 92.9   39%Heat Resistant 20 1.40% 1.5 0.62% Accelerator Foaming Agent 0.95 0.07%0.048 0.02% Pregelatinized 18 1.26% 20 8.29% Starch Sodium 2.14 0.15%0.27 0.11% Trimetaphosphate Retarder 0.48 0.03% 0.025 0.01% Dispersant2.4 0.17% 0.09 0.04% Alum 0.8 0.06% 0.052 0.02% Glass Fiber 2 0.14% 0.20.08% Dextrose 1.2 0.08% 0.12 0.05% Water 591 41.27%  126   52% Total:1432  100% 241  100%

Boards 9A and 9B were each prepared on a high speed machine using a mainpin mixer to combine wet and dry ingredients in a continuous process, asdescribed in Example 3, to form a continuous ribbon of board precursor,with core slurry deposited between two sheets of paper. A concentratedlayer was used to prepare Boards 9A and 9B with the aid of a secondaryboard mixer to blend wet and dry ingredients. This concentrated layerslurry was applied to the face paper using an application roller, withthe core slurry deposited thereon from a discharge conduit from the mainmixer. The precursors were processed and kiln dried to form the finalboards, 9A and 9B. Properties and dimensions of the boards are set forthin Table 23.

TABLE 23 Overall Board Details Board Nail Pull Actual Thickness BoardWeight Result Thickness Board (in) (lbs/MSF) (lbs force) (pcf) Board 9A0.5 1110 75.6 0.035 Board 9B 0.5 1109 80.2 0.04

This example shows a benefit of using a concentrated layer. Increasingthe thickness of the concentrated layer enhanced strength, although bothBoards 9A and 9B were sufficiently strong and effective. Both boardscontained higher concentration of enhancing additive (starch) in theconcentrated layer. As seen in Table 23, Board 9A demonstrated lowernail pull as compared with Board 9B. In this regard, Board 9A differedfrom Board 9B in that Board 9A was prepared using a lower speed on theapplication roller, resulting in a thinner concentrated layer, whileBoard 9B was prepared using a higher speed on the application roller,resulting in a thicker concentrated layer. The results shown in Table 23indicate that increased starch concentration in the concentrated layer,as well as concentrated layer thickness can be used to modify nail pullresults.

EXAMPLE 10

This example demonstrates that the concentrated layer enhances nail pullperformance at a board weight target of 1,100 lbs/MSF (about 5370 g/m²),Two boards were prepared, Board 10A and Board 10B. Board 10B did notcontain a concentrated layer, while Board 10A did. The slurrycompositions for preparing Boards 10A and 10B are set forth in Tables 24and 25, respectively, The compositions were prepared as described inExample 3.

TABLE 24 Composition for Board 10A Core Concentrated Layer Weight WeightIngredient (lbs/MSF) Wt. % (lbs/MSF) Wt. % Stucco 790   56% 98 41.6%Heat Resistant 17 1.20% 2.7 1.15% Accelerator Foaming Agent 0.88 0.06%0.044 0.02% Pregelatinized 18 1.27% 20  8.5% Starch Sodium 2.14 0.15%0.27 0.11% Trimetaphosphate Retarder 0.48 0.03% 0.03 0.01% Dispersant2.2 0.15% 0.09 0.04% Alum 0.8 0.06% 0.052 0.02% Glass fiber 2 0.14% 0.20.08% Dextrose 1.4 0.10% 0.14 0.06% Water 585 41.20%  114 48.4% Total:1420  100% 236  100%

TABLE 25 Composition for Board 10B Core Concentrated Layer Weight WeightIngredients (lbs/MSF) Wt. % (lbs/MSF) Wt. % Stucco 817   53% N/A N/AHeat Resistant 20 1.30% N/A N/A Accelerator Foaming Agent 0.85 0.06% N/AN/A Pregelatinized 20 1.30% N/A N/A Starch Sodium 2.14 0.14% N/A N/ATrimetaphosphate Retarder 0.48 0.03% N/A N/A Dispersant 2 0.13% N/A N/AAlum 0.9 0.06% N/A N/A Glass Fiber 0 0.00% N/A N/A Dextrose 0 0.00% N/AN/A Water 678.1 43.99%  N/A N/A Total: 1541  100% N/A N/A

Boards 10A and 10B were each prepared on a high speed machine using amain pin mixer to combine wet and dry ingredients in a continuousprocess, as described in Example 3, to form a continuous ribbon of boardprecursor, with core slurry deposited between two sheets of paper. Aconcentrated layer was used to prepare Boards 10A with the aid of asecondary board mixer to blend wet and dry ingredients. Thisconcentrated layer slurry was applied to the face paper using anapplication roller, with the core slurry deposited thereon from adischarge conduit from the main mixer. The precursors were processed andkiln dried to form the final boards, 10A and 10B. Properties anddimensions of the boards are set forth in Table 26.

TABLE 26 Concentrated Overall Board Details Layer Details Board BoardNail Pull Formulated Dry Thickness Weight Result Thickness Density Board(in) (lbs/MSF) (lbs force) (in) (pcf) Board 10A 0.5 1098 76.4 0.035 41Board 10B 0.5 1096 70.2 N/A N/A

This example shows a benefit of using a concentrated layer. As seen inTable 26, Board 10A demonstrated a higher nail pull as compared withBoard 10B. In this regard, Board 10A differed from Board 10B in thatBoard 10A was prepared using a concentrated layer slurry that includedhigher concentrations of pregelatinized starch compared to the coreslurry, resulting in higher nail pull, while Board 10B did not contain aconcentrated layer. The results shown in Table 26 indicate aconcentrated layer containing high concentrations of pregelatinizedstarch can be used to increase nail pull.

All references, including publications, patent applications, andpatents, cited herein are hereby incorporated by reference to the sameextent as if each reference were individually and specifically indicatedto be incorporated by reference and were set forth in its entiretyherein.

The use of the terms “a” and “an” and “the” and “at least one” andsimilar referents in the context of describing the invention (especiallyin the context of the following claims) are to be construed to coverboth the singular and the plural, unless otherwise indicated herein orclearly contradicted by context. The use of the term “at least one”followed by a list of one or more items (for example, “at least one of Aand B”) is to be construed to mean one item selected from the listeditems (A or B) or any combination of two or more of the listed items (Aand B), unless otherwise indicated herein or clearly contradicted bycontext. As used herein, it will be understood that the term “bondingrelation” does not necessarily mean that two layers are in immediatecontact. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. Also, everywhere “comprising”(or its equivalent) is recited, the “comprising” is considered toincorporate “consisting essentially of” and “consisting of.” Thus, anembodiment “comprising” (an) element(s) supports embodiments “consistingessentially of” and “consisting of” the recited element(s), Everywhere“consisting essentially of” is recited is considered to incorporate“consisting of.” Thus, an embodiment “consisting essentially of” (an)element(s) supports embodiments “consisting of” the recited element(s).Recitation of ranges of values herein are merely intended to serve as ashorthand method of referring individually to each separate valuefalling within the range, unless otherwise indicated herein, and eachseparate value is incorporated into the specification as if it wereindividually recited herein. The term “exemplary” refers to an exampleand is not intended to suggest the best example. All methods describedherein can be performed in any suitable order unless otherwise indicatedherein or otherwise clearly contradicted by context. The use of any andall examples, or exemplary language (e.g., “such as”) provided herein,is intended merely to better illuminate the invention and does not posea limitation on the scope of the invention unless otherwise claimed. Nolanguage in the specification should be construed as indicating anynon-claimed element as essential to the practice of the invention.

Preferred embodiments of this invention are described herein, includingthe best mode known to the inventors for carrying out the invention.Variations of those preferred embodiments may become apparent to thoseof ordinary skill in the art upon reading the foregoing description. Theinventors expect skilled artisans to employ such variations asappropriate, and the inventors intend for the invention to be practicedotherwise than as specifically described herein. Accordingly, thisinvention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the invention unlessotherwise indicated herein or otherwise clearly contradicted by context.

1. A composite gypsum board comprising: (a) a board core comprising setgypsum formed from at least water, stucco, and optionally, an enhancingadditive, the core defining a first core face; and (b) a concentratedlayer thrilled from at least water, stucco, and the enhancing additive,the concentrated layer disposed in bonding relation to the first coreface; wherein: (i) when the enhancing additive is included in formingthe board core, the enhancing additive is included in a higherconcentration in forming the concentrated layer than in forming theboard core, (ii) the board core has a thickness greater than thethickness of the concentrated layer, and (iii) the concentrated layerhas an average core hardness that is at least about 1.5 times greaterthan the average core hardness of the board core.
 2. The compositegypsum board of claim 1, wherein the concentrated layer is formed fromat least about 1.2 times the enhancing additive used in forming theboard core.
 3. The composite gypsum board of claim 1, wherein the boardhas a density of about 33 pcf (about 530 kg/m³) or less, and the boardhas a nail pull resistance according to ASTM C473-10, Method B of atleast about 68 lbs of force.
 4. The composite gypsum board of claim 1,wherein the enhancing additive comprises starch.
 5. The composite gypsumboard of claim 4, wherein the starch comprises a pregelatinized starchhaving a viscosity of from about 20 centipoise to about 700 centipoisewhen the viscosity is measured while the starch is subjected toconditions according to the VMA method.
 6. The composite gypsum board ofclaim 1, wherein the board core has a dry density of about 30 pcf orless.
 7. The composite gypsum board of claim 1, wherein the concentratedlayer has a Young's modulus that is at least about 1.5 times higher thana Young's modulus of the board core
 8. A composite gypsum boardcomprising; (a) a board core comprising set gypsum formed from at leastwater, stucco, and optionally, an enhancing additive, the core having adry density, the core defining first and second core faces in opposingrelation; and (b) a concentrated layer formed from at least water,stucco, and the enhancing additive, the concentrated layer disposed inbonding relation to the first core face; wherein: (i) when the enhancingadditive is present in forming the core, the concentrated layer isformed from at least about 1.2 times the enhancing additive used informing the board core, (ii) the board core has a dry density of about30 pcf or less, and (iii) the concentrated layer has a higher drydensity than the board core dry density.
 9. The composite gypsum boardof claim 8, wherein the board has a density of about 33 pcf (about 530kg/m³) or less, and the board has a nail pull resistance according toASTM C473-1.0, Method B of at least about 68 lbs of force.
 10. Thecomposite gypsum board of claim 8, wherein the enhancing additivecomprises starch.
 11. The composite gypsum board of claim 10, whereinthe starch comprises a pregelatinized starch having a viscosity of fromabout 20 centipoise to about 700 centipoise when the viscosity ismeasured while the starch is subjected to conditions according to theVMA method.
 12. The composite gypsum board of claim 8 wherein the boardcore has a dry density of about 30 pcf or less.
 13. The composite gypsumboard of claim 8, wherein the concentrated layer has a Young's modulusthat is at least about 1.5 times higher than a Young's modulus of theboard core.
 14. The composite gypsum board of claim 8, wherein thedensity differential between the concentrated layer and the board coreis at least about 8 pcf (about 130 kg/m³).
 15. The composite gypsumboard of claim 8, wherein the concentrated layer is further formed fromglass fiber.
 16. A composite gypsum board comprising: (a) a board corecomprising set gypsum formed from at least water, stucco, andoptionally, one or both of dispersant and/or polyphosphate, the corehaving a dry density, the core defining first and second core faces inopposing relation; and (b) a concentrated layer formed from at leastwater, stucco, and one or both of polyphosphate and dispersant, theconcentrated layer disposed in bonding relation to the first core face;wherein: (i) when the polyphosphate and/or dispersant is present informing the core, the polyphosphate and/or dispersant is included in ahigher concentration in forming the concentrated layer than in formingthe board core, and (ii) the concentrated layer has a higher dry densitythan the board core dry density.
 17. The composite gypsum board of claim16, wherein the concentrated layer is further from enhancing additive,and the board core is optionally further formed from enhancing additive,and wherein when the enhancing additive is included in forming the boardcore, the enhancing additive is included in a higher concentration informing the concentrated layer than in forming the board core.
 18. Thecomposite gypsum board of claim 16, wherein the board core has a drydensity of about 30 pcf or less.
 19. The composite gypsum board of claim16, wherein the board has a density of about 33 pcf (about 530 kg/m³) orless, and the board has a nail pull resistance according to ASTMC473-10, Method B of at least about 68 lbs of force.
 20. The compositegypsum board of claim 16, wherein the enhancing additive comprisesstarch.
 21. The composite gypsum board of claim 20, wherein the starchcomprises a pregelatinized starch having a viscosity of from about 20centipoise to about 700 centipoise when the viscosity is measured whilethe starch is subjected to conditions according to the VMA method.